How to Hide the "Simple Posts Order" Admin Menu

function plt_hide_simple_posts_order_menus() {
	//Hide the "Settings → Simple Posts Order" menu.
	remove_submenu_page('options-general.php', 'SimplePostsOrder');
}

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

Where do I put this code?