Remove usage of Rules module

[Ambient-Impact]

The primary reasons for this are that it doesn't seem like it'll have a Drupal 10 version soon (actually the dev release supports Drupal 10), is still in alpha after all this time, and introduces a lot of complexity that we arguably don't need since we don't regularly edit these things via the UI.

See also #1

https://www.drupal.org/project/rules

Short term, we could just remove the Rules module, disabling the actions it would trigger; longer term, we can re-implement these as generic event handlers/hooks or rethink the system entirely to use something with better UX than spam-all-the-emails.