feat: replace experimental add solana account with remote flag (#30487)

<!--
Please submit this PR as a draft initially.
Do not mark it as "Ready for review" until the template has been
completely filled out, and PR status checks have passed at least once.
-->

## **Description**

- [x] Removes experimental `Enable "Add Solana account"` setting
- [x] Adds remote feature flag fence
- [x] Enable feature in `flask - dev` 

<!--
Write a short description of the changes included in this pull request,
also include relevant motivation and context. Have in mind the following
questions:
1. What is the reason for the change?
2. What is the improvement/solution?
-->

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/30487?quickstart=1)

## **Related issues**

Fixes:

## **Manual testing steps**

1. Add `MANIFEST_OVERRIDES=.manifest-overrides.json` to the
`.metamaskrc`
2. Create a `.manifest-overrides.json` file 
3. Add the following content
```
{
  "_flags": {
    "remoteFeatureFlags": { "addSolanaAccount": true }
  }
}
```
4. Build
5. Modify the value to test both cases (enabled/disabled)

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**

<!-- [screenshots/recordings] -->

### **After**

<!-- [screenshots/recordings] -->

## **Pre-merge author checklist**

- [ ] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [x] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

app/scripts/controllers/preferences-controller.test.ts

@@ -875,19 +875,4 @@ describe('preferences controller', () => {
       );
     });
   });
-
-  describe('setSolanaSupportEnabled', () => {
-    const { controller } = setupController({});
-    it('has the default value as false', () => {
-      expect(controller.state.solanaSupportEnabled).toStrictEqual(false);
-    });
-
-    it('sets the solanaSupportEnabled property in state to true and then false', () => {
-      controller.setSolanaSupportEnabled(true);
-      expect(controller.state.solanaSupportEnabled).toStrictEqual(true);
-
-      controller.setSolanaSupportEnabled(false);
-      expect(controller.state.solanaSupportEnabled).toStrictEqual(false);
-    });
-  });
 });

app/scripts/controllers/preferences-controller.ts

@@ -142,9 +142,6 @@ export type PreferencesControllerState = Omit<
   ///: BEGIN:ONLY_INCLUDE_IF(build-flask)
   watchEthereumAccountEnabled: boolean;
   ///: END:ONLY_INCLUDE_IF
-  ///: BEGIN:ONLY_INCLUDE_IF(solana)
-  solanaSupportEnabled: boolean;
-  ///: END:ONLY_INCLUDE_IF
   ///: BEGIN:ONLY_INCLUDE_IF(bitcoin)
   bitcoinSupportEnabled: boolean;
   bitcoinTestnetSupportEnabled: boolean;
@@ -189,9 +186,6 @@ export const getDefaultPreferencesControllerState =
     openSeaEnabled: true,
     securityAlertsEnabled: true,
     watchEthereumAccountEnabled: false,
-    ///: BEGIN:ONLY_INCLUDE_IF(solana)
-    solanaSupportEnabled: false,
-    ///: END:ONLY_INCLUDE_IF
     bitcoinSupportEnabled: false,
     bitcoinTestnetSupportEnabled: false,
     ///: BEGIN:ONLY_INCLUDE_IF(keyring-snaps)
@@ -342,10 +336,6 @@ const controllerMetadata = {
     persist: true,
     anonymous: false,
   },
-  solanaSupportEnabled: {
-    persist: true,
-    anonymous: false,
-  },
   bitcoinSupportEnabled: {
     persist: true,
     anonymous: false,
@@ -665,20 +655,6 @@ export class PreferencesController extends BaseController<
   }
   ///: END:ONLY_INCLUDE_IF
 
-  ///: BEGIN:ONLY_INCLUDE_IF(solana)
-  /**
-   * Setter for the `solanaSupportEnabled` property.
-   *
-   * @param solanaSupportEnabled - Whether or not the user wants to
-   * enable the "Add a new Solana account" button.
-   */
-  setSolanaSupportEnabled(solanaSupportEnabled: boolean): void {
-    this.update((state) => {
-      state.solanaSupportEnabled = solanaSupportEnabled;
-    });
-  }
-  ///: END:ONLY_INCLUDE_IF
-
   ///: BEGIN:ONLY_INCLUDE_IF(bitcoin)
   /**
    * Setter for the `bitcoinSupportEnabled` property.

app/scripts/metamask-controller.js

@@ -3228,12 +3228,6 @@ export default class MetamaskController extends EventEmitter {
           preferencesController,
         ),
       ///: END:ONLY_INCLUDE_IF
-      ///: BEGIN:ONLY_INCLUDE_IF(solana)
-      setSolanaSupportEnabled:
-        preferencesController.setSolanaSupportEnabled.bind(
-          preferencesController,
-        ),
-      ///: END:ONLY_INCLUDE_IF
       ///: BEGIN:ONLY_INCLUDE_IF(bitcoin)
       setBitcoinSupportEnabled:
         preferencesController.setBitcoinSupportEnabled.bind(

shared/constants/metametrics.ts

@@ -651,7 +651,6 @@ export enum MetaMetricsEventName {
   BridgeLinkClicked = 'Bridge Link Clicked',
   BitcoinSupportToggled = 'Bitcoin Support Toggled',
   BitcoinTestnetSupportToggled = 'Bitcoin Testnet Support Toggled',
-  SolanaSupportToggled = 'Solana Support Toggled',
   CurrentCurrency = 'Current Currency',
   DappViewed = 'Dapp Viewed',
   DecryptionApproved = 'Decryption Approved',

test/data/mock-state.json

@@ -1961,7 +1961,6 @@
     "watchEthereumAccountEnabled": false,
     "bitcoinSupportEnabled": false,
     "bitcoinTestnetSupportEnabled": false,
-    "solanaSupportEnabled": false,
     "pendingApprovals": {
       "testApprovalId": {
         "id": "testApprovalId",

test/e2e/flask/solana/check-balance.spec.ts

@@ -8,7 +8,6 @@ describe('Check balance', function (this: Suite) {
     await withSolanaAccountSnap(
       {
         title: this.test?.fullTitle(),
-        solanaSupportEnabled: true,
         showNativeTokenAsMainBalance: true,
       },
       async (driver) => {
@@ -22,7 +21,6 @@ describe('Check balance', function (this: Suite) {
     await withSolanaAccountSnap(
       {
         title: this.test?.fullTitle(),
-        solanaSupportEnabled: true,
         showNativeTokenAsMainBalance: false,
       },
       async (driver) => {
@@ -36,7 +34,6 @@ describe('Check balance', function (this: Suite) {
     await withSolanaAccountSnap(
       {
         title: this.test?.fullTitle(),
-        solanaSupportEnabled: true,
         showNativeTokenAsMainBalance: true,
         mockCalls: true,
       },
@@ -51,7 +48,6 @@ describe('Check balance', function (this: Suite) {
     await withSolanaAccountSnap(
       {
         title: this.test?.fullTitle(),
-        solanaSupportEnabled: true,
         showNativeTokenAsMainBalance: false,
         mockCalls: true,
       },