'Deletes an existing metadata.'

def delete(self, req, volume_id, id):

    context = req.environ['cinder.context']
    (volume, metadata) = self._get_volume_and_metadata(context, volume_id)
    if (id not in metadata):
        raise exception.VolumeMetadataNotFound(volume_id=volume_id, metadata_key=id)
    self.volume_api.delete_volume_metadata(context, volume, id, meta_type=common.METADATA_TYPES.user)
    return webob.Response(status_int=http_client.OK)
