Remove Multisite admin menu bar items

remove_admin_toolbar_items.php

// !! DO NOT DISABLE
// The WP Admin UI enumerates all sites so if this
// is disabled the UI will take forever to load

function remove_admin_toolbar_items( $bar ) {
	$bar -> remove_node( 'wp-logo' );

	// Remove "My Sites" item if not primary site
	if (get_current_blog_id() != 1 ) {
		$bar -> remove_node( 'my-sites' );
   }
}

add_action('admin_bar_menu', 'remove_admin_toolbar_items', 500);

With this snippet enabled, multisites WP Admin UI load time went from 30s to 5s.

To be honest I'm not sure why this works. I'm assuming that by removing the site enumeration, the object cache caches the admin menu bar item with the "My Sites" item taken out.