How to Hide the "WP Realtime Sitemap" Admin Menu

function plt_hide_wp_realtime_sitemap_menus() {
	//Hide the "Settings → WP Realtime Sitemap" menu.
	remove_submenu_page('options-general.php', 'wp-realtime-sitemap.php');
}

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

Where do I put this code?