rxgroups/src/main/java/com/airbnb/rxgroups/ObservableGroup.java
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);
    }
  }
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);
    }
  }
Removes the supplied {@link Observable} from this group and cancels it subscription. No more
events will be delivered to its subscriber.