If you're just wanting to shut the request up and aren't actually trying to display a certain favicon you can do:

  <link rel=icon href=data:>

With the bonus you've probably already remembered how to reconstruct this on demand just by reading this comment. It is "invalid" data but so is your example on Safari and Firefox instead of Chromium based browsers. It doesn't matter as much because that problem is local and silent in the logs, unlike the request.