code: func (cgi *ConsumergroupInstance) Deregister() error {
  	node := fmt.Sprintf("%s/consumers/%s/ids/%s", cgi.cg.kz.conf.Chroot, cgi.cg.Name, cgi.ID)
  	exists, stat, err := cgi.cg.kz.conn.Exists(node)
  	if err != nil {
  		return err
  	} else if !exists {
  		return ErrInstanceNotRegistered
  	}
  
  	err = cgi.cg.kz.conn.Delete(node, stat.Version)
  	if err == zk.ErrNoNode {
  		return ErrInstanceNotRegistered
  	}
  	return err
  }
docs: // Deregister removes the registration of the instance from zookeeper.