Attempts to remove the directory named by dirname. The directory must be empty, and the relevant permissions must permit this. 成功回傳TRUE失敗回傳FALSE。
備注: As of PHP 5.0.0 rmdir() can also be used with some URL wrappers. Refer to 附錄 L for a listing of which wrappers support rmdir().
備注: The context parameter was added as of PHP 5.0.0.
備注:當安全模式開啟,PHP會檢查執行的腳本和要操作的檔案或目錄是否有相同的UID(擁有者)