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'         );

To remove the [rest_output_link_header](https://developer.wordpress.org/reference/functions/rest_output_link_header/)

    remove_action( 'template_redirect', 'rest_output_link_header', 11 );


Reference

* [wp_oembed_add_discovery_links](https://developer.wordpress.org/reference/functions/wp_oembed_add_discovery_links/)
* [rest_output_link_wp_head](https://developer.wordpress.org/reference/functions/rest_output_link_wp_head/)
* [rest_output_link_header](https://developer.wordpress.org/reference/functions/rest_output_link_header/)