How to Hide the "Custom Functions" Admin Menu

function plt_hide_custom_functions_starter_kit_menus() {
	//Hide the "Tools → Custom Functions" menu.
	remove_submenu_page('tools.php', 'custom-functions-admin-menu-settings');
}

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

Where do I put this code?