MM-27007 Remove automatic sidebar migration (#15087)

* MM-27007 Add migration of favorited channels to CreateInitialSidebarCategories

* MM-27007 Rewrite migrateFavortitesToSidebarT to use ROW_NUMBER() when available

* MM-27007 Remove automatic sidebar migration

* Remove old i18n strings

* Fix typo

* Address feedback

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/migration.go

@@ -17,6 +17,4 @@ const (
 	MIGRATION_KEY_ADD_MANAGE_GUESTS_PERMISSIONS               = "add_manage_guests_permissions"
 	MIGRATION_KEY_CHANNEL_MODERATIONS_PERMISSIONS             = "channel_moderations_permissions"
 	MIGRATION_KEY_ADD_USE_GROUP_MENTIONS_PERMISSION           = "add_use_group_mentions_permission"
-
-	MIGRATION_KEY_SIDEBAR_CATEGORIES_PHASE_2 = "migration_sidebar_categories_phase_2"
 )