<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _unwatch_file(self, filepath, trigger_event=True):
 """ Removes the file from the internal watchlist if exists. """

        if filepath not in self._watched_files:
            return
        if trigger_event:
            self.trigger_deleted(filepath)
        del self._watched_files[filepath]