How to Hide WP Maintenance Admin Menus

function plt_hide_wp_maintenance_menus() {
	//Hide "WP Maintenance".
	remove_menu_page('wp-maintenance');
	//Hide "WP Maintenance → General".
	remove_submenu_page('wp-maintenance', 'wp-maintenance');
	//Hide "WP Maintenance → Colors & Fonts".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-colors');
	//Hide "WP Maintenance → Pictures".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-picture');
	//Hide "WP Maintenance → CountDown".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-countdown');
	//Hide "WP Maintenance → CSS Style".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-css');
	//Hide "WP Maintenance → SEO".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-seo');
	//Hide "WP Maintenance → Social Networks".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-socialnetworks');
	//Hide "WP Maintenance → Footer".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-footer');
	//Hide "WP Maintenance → Settings".
	remove_submenu_page('wp-maintenance', 'wp-maintenance-settings');
}

add_action('admin_menu', 'plt_hide_wp_maintenance_menus', 11);

Where do I put this code?