Clears files in the download session temporary folder.
If the method succeeds, the return value is true. If the method fails, the return value is
false. To get extended error
information, call GetLastError and GetLastErrorDesc methods.
The download session temporary folder is specified with the DownloadSessionTempSubfolder
property. Unless the AutoRemoveCompletedFiles
property is set to true, you have to call this method to clear files in the
download session temporary folder upon the successful download.