HOW TO: Remove json/ rest/ API calls from header

// 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 );

// Remove the REST API endpoint.
remove_action( 'rest_api_init', 'wp_oembed_register_route' );

// Turn off oEmbed auto discovery.
add_filter( 'embed_oembed_discover', '__return_false' );

// Don't filter oEmbed results.
remove_filter( 'oembed_dataparse', 'wp_filter_oembed_result', 10 );

// Remove oEmbed discovery links.
remove_action( 'wp_head', 'wp_oembed_add_discovery_links' );

// Remove oEmbed-specific JavaScript from the front-end and back-end.
remove_action( 'wp_head', 'wp_oembed_add_host_js' );

// Remove all embeds rewrite rules.
add_filter( 'rewrite_rules_array', 'disable_embeds_rewrites' );