Get rid of any lingering watchers and remove from list

def unwatch(self):
        """Get rid of any lingering watchers and remove from list"""
        if self.watchers is not None:
            unwatched = []
            for watcher in self.watchers:
                watcher.inst.param.unwatch(watcher)
                unwatched.append(watcher)
            self.watchers = [w for w in self.watchers if w not in unwatched]