(PHP 5)
streamWrapper::unlink — Delete a file
This method is called in response to unlink().
Note:
In order for the appropriate error message to be returned this method should not be defined if the wrapper does not support removing files.
The file URL which should be deleted.
成功时返回 TRUE， 或者在失败时返回 FALSE.
Emits E_WARNING if call to this method fails (i.e. not implemented).
Note:
The streamWrapper->context property is updated if a valid context is passed to the caller function.