Flarum\Core\Notification\NotificationSyncer::delete PHP Method

    public function delete(BlueprintInterface $blueprint)
    {
        Notification::where($this->getAttributes($blueprint))->update(['is_deleted' => true]);
    }

 /**
  * @param \Flarum\Event\DiscussionWasRenamed $event
  */
 public function whenDiscussionWasRenamed(DiscussionWasRenamed $event)
 {
     $post = DiscussionRenamedPost::reply($event->discussion->id, $event->actor->id, $event->oldTitle, $event->discussion->title);
     $post = $event->discussion->mergePost($post);
     if ($event->discussion->start_user_id !== $event->actor->id) {
         $blueprint = new DiscussionRenamedBlueprint($post);
         if ($post->exists) {
             $this->notifications->sync($blueprint, [$event->discussion->startUser]);
         } else {
             $this->notifications->delete($blueprint);
         }
     }
 }