code: func (u *UserCommand) Delete(client auth.ClientI) error {
  	for _, l := range strings.Split(u.login, ",") {
  		if err := client.DeleteUser(l); err != nil {
  			return trace.Wrap(err)
  		}
  		fmt.Printf("User '%v' has been deleted\n", l)
  	}
  	return nil
  }
docs: // Delete deletes teleport user(s). User IDs are passed as a comma-separated
  // list in UserCommand.login