'Unschedules a watch.
:param watch:
The watch to unschedule.
:type watch:
An instance of :class:`ObservedWatch` or a subclass of
:class:`ObservedWatch`'

def unschedule(self, watch):

    with self._lock:
        emitter = self._emitter_for_watch[watch]
        del self._handlers[watch]
        self._remove_emitter(emitter)
        self._watches.remove(watch)
