Remove support for godep and dep (bazel-contrib#1541)

These 2 package managers were archived a while ago
- godep: Feb 26, 2019 (more than 4 years ago)
- dep: Sep 09, 2020 (almost 3 years ago)

Since then, the community has largely adopted Go Module as the
canonicaly package manager.

Removing these old package managers to make it easier to maintain
Gazelle in the long run.
This also let use remove the dependency on pelletier/go-toml package.

(1): https://github.com/golang/dep
(2): https://github.com/tools/godep

Design.rst

@@ -515,8 +515,6 @@ github.com/bazelbuild/buildtools/build
 github.com/bazelbuild/rules_go
   Used to build and test Gazelle through Bazel. Gazelle can aslo be built on its
   own with the Go SDK.
-github.com/pelletier/go-toml
-  Used to import dependencies from dep Gopkg.lock files.
 golang.org/x/tools/vcs
   Used during dependency resolution to determine the repository prefix for a
   given import path. This uses the network.

MODULE.bazel

@@ -12,7 +12,10 @@ bazel_dep(name = "rules_proto", version = "4.0.0")
 go_sdk = use_extension("@io_bazel_rules_go//go:extensions.bzl", "go_sdk")
 
 # Known to exist since it is instantiated by rules_go itself.
-use_repo(go_sdk, go_sdk = "go_default_sdk")
+use_repo(
+    go_sdk,
+    go_sdk = "go_default_sdk",
+)
 
 non_module_deps = use_extension("//internal/bzlmod:non_module_deps.bzl", "non_module_deps")
 use_repo(
@@ -35,7 +38,6 @@ use_repo(
     "com_github_bmatcuk_doublestar_v4",
     "com_github_fsnotify_fsnotify",
     "com_github_google_go_cmp",
-    "com_github_pelletier_go_toml",
     "com_github_pmezard_go_difflib",
     "org_golang_x_mod",
     "org_golang_x_sync",

README.rst

@@ -564,8 +564,8 @@ The following flags are accepted:
 The ``update-repos`` command updates repository rules.  It can write the rules
 to either the WORKSPACE (by default) or a .bzl file macro function.  It can be
 used to add new repository rules or update existing rules to the specified
-version. It can also import repository rules from a ``go.mod``, ``go.work`` or a
-``Gopkg.lock`` file.
+version. It can also import repository rules from a ``go.mod`` or a ``go.work``
+file.
 
 .. code:: bash
 
@@ -596,7 +596,7 @@ The following flags are accepted:
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+
 | Import repositories from a file as `go_repository`_ rules. These rules will be added to the bottom of the WORKSPACE file or merged with existing rules. |
 |                                                                                                                                                         |
-| The lock file format is inferred from the file name. ``go.mod``, ``go.work` and, ``Gopkg.lock`` (the dep lock format) are all supported.                |
+| The lock file format is inferred from the file name. ``go.mod`` and ``go.work` are all supported.                                                       |
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+
 | :flag:`-repo_root dir`                                                                                   |                                              |
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+
@@ -612,7 +612,7 @@ The following flags are accepted:
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+
 | :flag:`-prune true|false`                                                                                | :value:`false`                               |
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+
-| When true, Gazelle will remove `go_repository`_ rules that no longer have equivalent repos in the ``Gopkg.lock``/``go.mod`` file.                       |
+| When true, Gazelle will remove `go_repository`_ rules that no longer have equivalent repos in the ``go.mod`` file.                                      |
 |                                                                                                                                                         |
 | This flag can only be used with ``-from_file``.                                                                                                         |
 +----------------------------------------------------------------------------------------------------------+----------------------------------------------+

WORKSPACE

@@ -68,7 +68,6 @@ register_unittest_toolchains()
 # gazelle:repository go_repository name=com_github_golang_mock importpath=github.com/golang/mock
 # gazelle:repository go_repository name=com_github_golang_protobuf importpath=github.com/golang/protobuf
 # gazelle:repository go_repository name=com_github_google_go_cmp importpath=github.com/google/go-cmp
-# gazelle:repository go_repository name=com_github_pelletier_go_toml importpath=github.com/pelletier/go-toml
 # gazelle:repository go_repository name=com_github_pmezard_go_difflib importpath=github.com/pmezard/go-difflib
 # gazelle:repository go_repository name=com_github_prometheus_client_model importpath=github.com/prometheus/client_model
 # gazelle:repository go_repository name=com_github_yuin_goldmark importpath=github.com/yuin/goldmark