How to Hide the "MP-Ukagaka" Admin Menu

function plt_hide_mp_ukagaka_menus() {
	//Hide the "Settings → MP-Ukagaka" menu.
	remove_submenu_page('options-general.php', 'mp-ukagaka/options.php');
}

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

Where do I put this code?