rxgroups/src/main/java/com/airbnb/rxgroups/ObservableGroup.java
public void cancelAndRemove(Observer<?> observer, String observableTag) {
    cancelAndRemove(Utils.getObserverTag(observer), observableTag);
  }
public void cancelAndRemove(Observer<?> observer, String observableTag) {
    cancelAndRemove(Utils.getObserverTag(observer), observableTag);
  }
Removes the {@link Observable} identified by {@code observableTag} for the given
{@link Observer} and cancels it subscription.
No more events will be delivered to its subscriber.
<p>If no Observable is found for the provided {@code observableTag}, nothing happens.