Destroy associated worker tasks and notifications
Summary: Fixes T7107. When destroying an object, destroy associated worker tasks and notifications.
Test Plan:
# Manually updated the `phabricator_worker.worker_activetask` table by setting `objectPHID` to the desired object.
# Removed object with `./bin/remove destroy`.
# Queried `phabricator_worker.worker_activetask` table.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7107
Differential Revision: https://secure.phabricator.com/D12822