Event logs: User role assignments not working

`import ggrc.services.util` was throwing an exception. From what I can tell the `service_for` function has moved to ggrc.utils.

The new code also makes sure `related_object_id` is defined.

This fixes the issue [#57618116](https://www.pivotaltracker.com/story/show/57618116), but the logs currently don't show on which Program the mapping occurred.