code: func (s *Service) Unregister(reg fab.Registration) {
  	if err := s.Submit(dispatcher.NewUnregisterEvent(reg)); err != nil {
  		logger.Warnf("Error unregistering: %s", err)
  	}
  }
docs: // Unregister unregisters the given registration.
  // - reg is the registration handle that was returned from one of the RegisterXXX functions