code: private void cancelAndRemove(String observerTag, String observableTag) {
      Map<String, ManagedObservable<?>> observables = getObservablesForObserver(observerTag);
      ManagedObservable<?> managedObservable = observables.get(observableTag);
      if (managedObservable != null) {
        managedObservable.cancel();
        observables.remove(observableTag);
      }
    }
docs: Removes the supplied {@link Observable} from this group and cancels it subscription. No more
  events will be delivered to its subscriber.