`delete_module` is used for capa problems, also - it is vital for courses which have students who have gotten state corrupted.  This happens, for example, with beta testers, who see different versions of the problem, but the `url_name` stays unchanged, thus leaving their state out of sync.

This PR apparently breaks the ability to delete capa problem state, because `capa_module` does not have a `reset_score` method.