Removed recurcive stop method from WaitingState.

When PlayListController is in WaitingState and we are trying to play a clip via javascript like:
```
player.fp_play(clip_descriptor)
```
WaitingState.stop method is called, so execution context waits for infinite recursion to stop.

I can't say if this method was needed for some purposes, because I could not find change history in google code. At least, I did not find any direct calls to this method in code. So, I removed it.