code: @MainThread
      public void removeObserver(@NonNull final Observer<T> observer) {
          assertMainThread("removeObserver");
          ObserverWrapper removed = mObservers.remove(observer);
          if (removed == null) {
              return;
          }
          removed.detachObserver();
          removed.activeStateChanged(false);
      }
docs: Removes the given observer from the observers list.
  
  @param observer The Observer to receive events.