Fixes issue where layer model wasn't being updated in NSBFunctionView

Hey Nacho, 

I spotted this just after we had the discussion over at https://gist.github.com/d-ronnqvist/11266321 about removedOnCompletion. I believe this fixes the issue where the layer model remains unchanged despite the animation. 

I wasn't sure whether to send this pull request as it looks like this code is no longer maintained and I don't want to come across as a jerk, just wanted to help spread (what I now know is) the correct way :)

Cheers.

Sam.