I see in filters.php 

`add_action( 'wp_head', 'rest_output_link_wp_head', 10, 0 );`

Which makes me think this should do the trick to remove `rel='https://api.w.org/'`.

    remove_action( 'wp_head',      'rest_output_link_wp_head'              );

The rest... * *cough* * seem to be in default-filters.php

    remove_action( 'wp_head',      'wp_oembed_add_discovery_links'         );