MM-53358: Revert Threads Everywhere (#23882)

Remove changes related to the unshipped threads everywhere feature, including commits b8da473da7 and 9f9e19e05d.

Since a version of Playbooks shipped calling this experimental API, keep a `nil` implementation to avoid breaking compatibility. We remove the hooks altogether, but keep the numbering again to avoid breaking compatbility.

Fixes: https://mattermost.atlassian.net/browse/MM-53358

server/i18n/en.json

@@ -4931,14 +4931,6 @@
     "id": "app.cloud.upgrade_plan_bot_message_single",
     "translation": "{{.UsersNum}} member of the {{.WorkspaceName}} workspace has requested a workspace upgrade for: "
   },
-  {
-    "id": "app.collection.add_collection.exists.app_error",
-    "translation": "Collection type already exists."
-  },
-  {
-    "id": "app.collection.add_topic.exists.app_error",
-    "translation": "Topic type already exists."
-  },
   {
     "id": "app.command.createcommand.internal_error",
     "translation": "Unable to save the command."