/**
  * Remove subscription
  *
  * @param User $user
  * @param ProjectObject $object
  * @return boolean
  */
 function unsubscribe($user, $object)
 {
     if (!$object->can_have_subscribers) {
         return new InvalidParamError('$object', $object, '$object does not support subscribers', true);
     }
     // if
     Subscriptions::dropUserCache($user);
     return Subscriptions::delete(array('user_id = ? AND parent_id = ?', $user->getId(), $object->getId()));
 }