Minor Sandcastle example cleanup

Low-hanging fruit from #1685.

Lots more to come, of course.

This also changes `removeEventListener` to return a boolean indicating if the event was removed instead of throwing an exception.  This is consistent with `remove` on all our collections and makes the camera ICRF examples cleaner.
It would be nice if this was easier.  Resetting to home view shouldn't require simulating a button press.  I'll add an issue for the future.