don't trigger onExitTransitionDidStart

I can understand what you are saying, but let's imagine my game is made in a way that most cleanup is made in onExitTransitionDidStart and not on onExit, because I replace scenes using a TransitionScene and I don't want to generate any conflicts between the two scenes. (imagine my nodes use platform-specific services like Text-to-speech, audio recording, etc). 

This way, if I purge the director, my onExitTransitionDidStart methods will not be called and I will end up with resources that were not properly cleaned.

Of course I could move all that logic to onEnter/onExit instead of onExitTransitionDidStart/onEnterTransitionDidFinish but it just doesn't seem natural.