Fix AccountDeletionWorker crashing and clogging sidekiq queues (#15380)
* Fix account deletion workers being queued multiple times for a single account
* Fix poll votes being unnecessarily instantiated on poll deletion
* Fix favourites being unnecessarily instantiated on status deletion
* Remove inaccurate comments
* Delete polls instead of destroying them
Co-authored-by: Claire <claire.github-309c@sitedethib.com>