'Deletes a generic volume group.
:param context: the context
:param group: the group object to be deleted
:param volumes: the list of volumes in the generic group to be deleted
:returns: dict -- modelUpdate
:returns: list -- list of volume model updates
:raises: NotImplementedError'

def delete_group(self, context, group, volumes):

    LOG.info('Delete    generic    volume    group:    %(group)s.', {'group': group.id})
    if (not volume_utils.is_group_a_cg_snapshot_type(group)):
        raise NotImplementedError()
    (model_update, volumes_model_update) = self._delete_group(group, volumes)
    return (model_update, volumes_model_update)
