How to Hide the "Add Code to Head" Admin Menu

function plt_hide_add_code_to_head_menus() {
	//Hide the "Settings → Add Code to Head" menu.
	remove_submenu_page('options-general.php', 'acth_plugin');
}

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

Where do I put this code?