Tools like Perfmatters can toggle off the wlwmanifest link in your site's header.
If you are seeing 404 errors for this file on a non-WordPress site, you can safely ignore them; it just means a bot guessed incorrectly that you were using WordPress.
While you can delete the file from /wp-includes/ , it will often reappear when you update WordPress.
WordPress continues to include this file for backward compatibility, although it is virtually unused by modern bloggers. Common Actions to Take