method unlisten

Source

void unlisten(callback(ValueUpdate update)) {
  if (callbacks.containsKey(callback)) {
    int cacheLevel = callbacks.remove(callback);
    if (callbacks.isEmpty) {
      requester._subscription.removeSubscription(this);
    } else if (cacheLevel == currentQos && currentQos > 1) {
      updateQos();
    }
  }
}