Fix processing of remote Delete activities (#16084)

* Add tests

* Ensure deleted statuses are marked as such

* Save some redis memory by not storing URIs in delete_upon_arrival values

* Avoid possible race condition when processing incoming Deletes

* Avoid potential duplicate Delete forwards

* Lower lock durations to reduce issues in case of hard crash of the Rails process

* Check for `lock.aquired?` and improve comment

* Refactor RedisLock usage in app/lib/activitypub

* Fix using incorrect or non-existent sender for relaying Deletes

app/services/remove_status_service.rb

@@ -16,6 +16,8 @@ class RemoveStatusService < BaseService
     @account  = status.account
     @options  = options
 
+    @status.discard
+
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
         remove_from_self if @account.local?