Drop UsersGroup orphans using `rails runner`

lib/tasks/gitlab/check.rake

@@ -186,6 +186,10 @@ namespace :gitlab do
       print "Database contains orphaned UsersGroups? ... "
       if UsersGroup.where("user_id not in (select id from users)").count > 0
         puts "yes".red
+        try_fixing_it(
+          "You can delete the orphaned records using something along the lines of:",
+          sudo_gitlab("bundle exec rails runner -e production 'UsersGroup.where(\"user_id NOT IN (SELECT id FROM users)\").delete_all'")
+        )
       else
         puts "no".green
       end