How to Hide the "Same but Different" Admin Menu

function plt_hide_same_but_different_menus() {
	//Hide the "Appearance → Same but Different" menu.
	remove_submenu_page('themes.php', 'same-but-different_settings');
}

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

Where do I put this code?