Destroy notifications properly from `bin/remove destroy`
Summary: Fixes T8237. This table is unusual and doesn't have an `id` column, so `delete()` doesn't actually know how to delete records and fails.
Test Plan:
- Used `bin/remove destroy` to destroy an object with notifications, as per T8237.
- Applied patch.
- Used `bin/remove destroy` to get a clean delete.
- Verified related notifications vanished from notification menu.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T8237
Differential Revision: https://secure.phabricator.com/D12907