Replace incorrect use of distinct with group (mastodon#14675)

Some uses of ActiveRecord::QueryMethods#distinct pass field names but they
are incorrect for the current version of Rails.

ActiveRecord::QueryMethods#group provides the expected behavior and
benefits performance. See commit 6da24aa.

app/controllers/api/v1/accounts/statuses_controller.rb

@@ -41,17 +41,7 @@ def permitted_account_statuses
   end
 
   def only_media_scope
-    Status.where(id: account_media_status_ids)
-  end
-
-  def account_media_status_ids
-    # `SELECT DISTINCT id, updated_at` is too slow, so pluck ids at first, and then select id, updated_at with ids.
-    # Also, Avoid getting slow by not narrowing down by `statuses.account_id`.
-    # When narrowing down by `statuses.account_id`, `index_statuses_20180106` will be used
-    # and the table will be joined by `Merge Semi Join`, so the query will be slow.
-    @account.statuses.joins(:media_attachments).merge(@account.media_attachments).permitted_for(@account, current_account)
-            .paginate_by_max_id(limit_param(DEFAULT_STATUSES_LIMIT), params[:max_id], params[:since_id])
-            .reorder(id: :desc).distinct(:id).pluck(:id)
+    Status.joins(:media_attachments).merge(@account.media_attachments.reorder(nil)).group(:id)
   end
 
   def pinned_scope

app/controllers/api/v1/timelines/public_controller.rb

@@ -30,9 +30,7 @@ def public_statuses
     )
 
     if truthy_param?(:only_media)
-      # `SELECT DISTINCT id, updated_at` is too slow, so pluck ids at first, and then select id, updated_at with ids.
-      status_ids = statuses.joins(:media_attachments).distinct(:id).pluck(:id)
-      statuses.where(id: status_ids)
+      statuses.joins(:media_attachments).group(:id)
     else
       statuses
     end