Fix bug mentioned in #1565 (#1954)

lib/tasks/mastodon.rake

@@ -100,7 +100,7 @@ namespace :mastodon do
       # only have a user record and an avatar record, with no files uploaded
       User.where('confirmed_at is NULL AND confirmation_sent_at <= ?', 2.days.ago).find_in_batches do |batch|
         Account.where(id: batch.map(&:account_id)).delete_all
-        batch.delete_all
+        User.where(id: batch.map(&:id)).delete_all
       end
     end
   end