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