Disable WordPress JSON/REST API and remove lines from source code / header

WordPress_Disable-JSON-REST-API.php

<?php // Copy and Paste snippet below into child-theme functions or custom plugin -- DELETE THIS LINE

// Disable WordPress JSON-REST API
function disable_json_api () {

  // Remove the REST API lines from the HTML Header
  remove_action( 'wp_head', 'rest_output_link_wp_head', 10 );
  remove_action( 'wp_head', 'wp_oembed_add_discovery_links', 10 );

  // Filters for WP-API version 1.x
  add_filter('json_enabled', '__return_false');
  add_filter('json_jsonp_enabled', '__return_false');

  // Filters for WP-API version 2.x
  add_filter('rest_enabled', '__return_false');
  add_filter('rest_jsonp_enabled', '__return_false');

}
add_action( 'after_setup_theme', 'disable_json_api' );