def cleanup(achalls):
    """Revert changes and shutdown after challenges complete.

        This method should be able to revert all changes made by
        perform, even if perform exited abnormally.

        :param list achalls: Non-empty (guaranteed) list of
            :class:`~certbot.achallenges.AnnotatedChallenge`
            instances, a subset of those previously passed to :func:`perform`.

        :raises PluginError: if original configuration cannot be restored

        """
