code: void stop(final Actor actor) {
      final Actor removedActor = directory.remove(actor.address());
  
      if (actor == removedActor) {
        removedActor.lifeCycle.stop(actor);
      }
    }
docs: Stop the given Actor and all its children. The Actor instance is first removed from
  the Directory of this Stage. (INTERNAL ONLY)
  @param actor the Actor to stop