code: func (gce *Cloud) DeleteInstanceGroup(name string, zone string) error {
  	op, err := gce.service.InstanceGroups.Delete(
  		gce.projectID, zone, name).Do()
  	if err != nil {
  		return err
  	}
  	return gce.waitForZoneOp(op, zone)
  }
docs: // DeleteInstanceGroup deletes an instance group.