Completes the asynchronous operation started in BeginDeleteDirectory.
Before calling BeginDeleteDirectory, you need to create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginDeleteDirectory returns. The callback method must accept the IAsyncResult returned by the BeginDeleteMultipleFiles method as a parameter. This parameter may then be passed to the EndDeleteDirectory method to complete the operation.