BB-8165: Remove Decrement Inventory settings from UI. (#8299)

* BB-8165: Remove Decrement Inventory settings from UI.
Next configuration options from System -> Configuration -> COMMERCE -> Inventory -> Product Options -> Product Inventory Options and related functionality:
Manage Inventory (yes/no)
Back-ordes (yes/no)
Inventory Threshold
Decrement inventory
should be removed.

src/Oro/Bundle/InventoryBundle/DependencyInjection/Configuration.php

@@ -9,10 +9,6 @@
 
 class Configuration implements ConfigurationInterface
 {
-    const MANAGE_INVENTORY = 'manage_inventory';
-    const INVENTORY_THRESHOLD = 'inventory_threshold';
-    const BACKORDERS = 'backorders';
-    const DECREMENT_INVENTORY = 'decrement_inventory';
     const MINIMUM_QUANTITY_TO_ORDER = 'minimum_quantity_to_order';
     const MAXIMUM_QUANTITY_TO_ORDER = 'maximum_quantity_to_order';
     const DEFAULT_MAXIMUM_QUANTITY_TO_ORDER = 100000;
@@ -43,10 +39,6 @@ public function getConfigTreeBuilder()
         SettingsBuilder::append(
             $rootNode,
             [
-                self::MANAGE_INVENTORY => ['type' => 'boolean', 'value' => false],
-                self::INVENTORY_THRESHOLD => ['type' => 'decimal', 'value' => 0],
-                self::BACKORDERS => ['type' => 'boolean', 'value' => false],
-                self::DECREMENT_INVENTORY => ['type' => 'boolean', 'value' => false],
                 self::MINIMUM_QUANTITY_TO_ORDER => ['type' => 'decimal', 'value' => null],
                 self::MAXIMUM_QUANTITY_TO_ORDER => [
                     'type' => 'decimal',