code: func (r *Registrar) DeleteRegistration() error {
  	if r == nil || r.user == nil {
  		return errors.New("acme: cannot unregister a nil client or user")
  	}
  
  	log.Infof("acme: Deleting account for %s", r.user.GetEmail())
  
  	return r.core.Accounts.Deactivate(r.user.GetRegistration().URI)
  }
docs: // DeleteRegistration deletes the client's user registration from the ACME server.