WordPress Tuning, jquery for defer loading and async loading of css files. But not for admin. It breaks then the wp editor.

functions.php

// remove all this Worpress nonsens for tuning and better performance.

add_filter('xmlrpc_enabled', '__return_false' );
add_filter('got_rewrite', '__return_true', 999);
add_filter('wp_get_attachment_image_attributes', 'ipwp_img_attr', 10, 2); function ipwp_img_attr($attr) { $attr['itemprop'] = 'image'; return $attr;}
add_filter('xmlrpc_methods', function($methods) { unset($methods['wp.getUsersBlogs']); return $methods; });
add_filter('wp_headers', 'FastWP_remove_x_pingback' ); function FastWP_remove_x_pingback( $headers ) { unset( $headers['X-Pingback'] ); return $headers;}

function disable_emojis() {remove_action( 'wp_head', 'print_emoji_detection_script', 7 );
remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
remove_action( 'wp_print_styles', 'print_emoji_styles');
remove_action( 'admin_print_styles', 'print_emoji_styles');	
remove_filter( 'the_content_feed', 'wp_staticize_emoji');
remove_filter( 'comment_text_rss', 'wp_staticize_emoji');	
remove_filter( 'wp_mail', 'wp_staticize_emoji_for_email');
add_filter( 'tiny_mce_plugins', 'disable_emojis_tinymce'); }
add_action( 'init', 'disable_emojis' );
function disable_emojis_tinymce( $plugins ) { if ( is_array( $plugins ) ) { return array_diff( $plugins, array( 'wpemoji' ) ); } else {return array(); } }

add_action('init', 'remheadlink'); function remheadlink() {remove_action('wp_head', 'rsd_link');
	remove_action('wp_head', 'wp_generator');
	remove_action('wp_head', 'index_rel_link');
	remove_action('wp_head', 'wlwmanifest_link');
	remove_action('wp_head', 'feed_links', 2);
	remove_action('wp_head', 'feed_links_extra', 3);
	remove_action('wp_head', 'parent_post_rel_link', 10, 0);
	remove_action('wp_head', 'start_post_rel_link', 10, 0);
	remove_action('wp_head', 'wp_shortlink_wp_head', 10, 0);
	remove_action('wp_head', 'wp_shortlink_header', 10, 0);
	remove_action('wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0); 
	remove_action('wp_head', 'wp_resource_hints', 2 );}

// disable it
add_filter( 'emoji_svg_url', '__return_false' );
function block_wp_embed() {wp_deregister_script('wp-embed'); } 
add_action('init', 'block_wp_embed');
add_action('init', 'stop_heartbeat', 1); 
function stop_heartbeat() {wp_deregister_script('heartbeat');}
remove_filter( 'the_content', 'wp_make_content_images_responsive' );

function reassign_jQuery() { 
wp_deregister_script( 'jquery' ); 
wp_deregister_script( 'jquery-core' ); 
wp_deregister_script( 'jquery-migrate' ); 
wp_register_script('jquery', get_stylesheet_directory_uri() . '/js/jquery.js', array(), null, true ); 
wp_enqueue_script('jquery');}
if ( ! is_admin() ) add_action('init', 'reassign_jQuery');

// https://github.com/filamentgroup/loadCSS
if ( ! is_admin() ) add_action('wp_head','add_load_css',7);
function add_load_css(){ ?><script><?php readfile(get_stylesheet_directory() . '/js/loadCSS.js'); ?></script><?php }
if ( ! is_admin() ) add_filter('style_loader_tag', 'link_to_loadCSS_script',9999,3);
function link_to_loadCSS_script($html, $handle, $href ) {
    $dom = new DOMDocument();
    $dom->loadHTML($html);
    $a = $dom->getElementById($handle.'-css');
    return "<script>loadCSS('" . $a->getAttribute('href') . "',0,'" . $a->getAttribute('media') . "');</script>\n";
}

// function to add defer or async to all scripts 
function js_async_attr($tag){ return str_replace( ' src', ' defer="defer" src', $tag ); } 
if ( ! is_admin() ) add_filter( 'script_loader_tag', 'js_async_attr', 10 );