Don't leave behind husk of remotely-deleted profile (#6159)

There's no reason for an Account record to persist after Delete->Actor is received. SuspendAccountService is necessary to make sure deleted toots get sent over streaming API properly and home feeds get cleaned up. By removing Account record, we can ensure that if in the future the account is restored remotely (or username reused), it can start with a clean slate.

app/lib/activitypub/activity/delete.rb

@@ -13,6 +13,7 @@ class ActivityPub::Activity::Delete < ActivityPub::Activity
 
   def delete_person
     SuspendAccountService.new.call(@account)
+    @account.destroy!
   end
 
   def delete_note