Remove WAIT_FOR_DELETE delay

Remove the delay for unassigning user from issue and merge requsts
after user membership has been removed

app/services/members/destroy_service.rb

@@ -2,8 +2,6 @@
 
 module Members
   class DestroyService < Members::BaseService
-    WAIT_FOR_DELETE = 1.hour
-
     def execute(member, skip_authorization: false, skip_subresources: false, unassign_issuables: false)
       raise Gitlab::Access::AccessDeniedError unless skip_authorization || can_destroy_member?(member)
 
@@ -72,7 +70,7 @@ module Members
       source_type = member.is_a?(GroupMember) ? 'Group' : 'Project'
 
       member.run_after_commit do
-        MembersDestroyer::UnassignIssuablesWorker.perform_in(WAIT_FOR_DELETE, member.user_id, member.source_id, source_type)
+        MembersDestroyer::UnassignIssuablesWorker.perform_async(member.user_id, member.source_id, source_type)
       end
     end
   end