code: func (p *Pinger) RemoveIP(ipaddr string) error {
  	addr := net.ParseIP(ipaddr)
  	if addr == nil {
  		return fmt.Errorf("%s is not a valid textual representation of an IP address", ipaddr)
  	}
  	p.mu.Lock()
  	delete(p.addrs, addr.String())
  	p.mu.Unlock()
  	return nil
  }
docs: // RemoveIP removes an IP address from Pinger. ipaddr arg should be a string
  // like "192.0.2.1".