function exclude_draft_pages_from_menu($items, $menu, $args) {
    foreach ($items as $key => $item) {
        if ('draft' === get_post_status($item->object_id)) {
            unset($items[$key]);
        }
    }
    return $items;
}
add_filter('wp_get_nav_menu_items', 'exclude_draft_pages_from_menu', 10, 3);