Change DeleteUserWorker to match CE

This changes DeleteUserWorker so its code is the same as in CE.

app/workers/delete_user_worker.rb

@@ -7,7 +7,7 @@ class DeleteUserWorker
     delete_user  = User.find(delete_user_id)
     current_user = User.find(current_user_id)
 
-    ::Users::DestroyService.new(current_user).execute(delete_user, options.symbolize_keys)
+    Users::DestroyService.new(current_user).execute(delete_user, options.symbolize_keys)
   rescue Gitlab::Access::AccessDeniedError => e
     Rails.logger.warn("User could not be destroyed: #{e}")
   end