Add migration to clear pending LogDestroyWorker jobs

WebHook::LogDestroyWorker was no-oped in !197625 (merged).

Per the handbook, we should now raise an MR containing a migration that clears any pending LogDestroyWorker jobs.

Deliverables

1. Raise an MR that clears pending LogDestroyWorker jobs.
2. Create an issue to delete the worker class.

https://docs.gitlab.com/development/sidekiq/compatibility_across_updates/#removing-worker-classes