Clean stale local refs so they don't appear as fileserver environments

def clean_stale_refs(self, local_refs=None):  # pylint: disable=arguments-differ
        '''
        Clean stale local refs so they don't appear as fileserver environments
        '''
        try:
            if pygit2.GIT_FETCH_PRUNE:
                # Don't need to clean anything, pygit2 can do it by itself
                return []
        except AttributeError:
            # However, only in 0.26.2 and newer
            pass
        if self.credentials is not None:
            log.debug(
                'The installed version of pygit2 (%s) does not support '
                'detecting stale refs for authenticated remotes, saltenvs '
                'will not reflect branches/tags removed from remote \'%s\'',
                PYGIT2_VERSION, self.id
            )
            return []
        return super(Pygit2, self).clean_stale_refs()