How to Hide the "Mime Types Plus" Admin Menu

function plt_hide_mime_types_plus_menus() {
	//Hide the "Settings → Mime Types Plus" menu.
	remove_submenu_page('options-general.php', 'MimeTypesPlus');
}

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

Where do I put this code?