Delete all expired taskset results.

def delete_expired(self, expires):
        """Delete all expired taskset results."""
        meta = self.model._meta
        with commit_on_success():
            self.get_all_expired(expires).update(hidden=True)
            cursor = self.connection_for_write().cursor()
            cursor.execute(
                'DELETE FROM {0.db_table} WHERE hidden=%s'.format(meta),
                (True, ),
            )