Deletes a Folder.
int DeleteFolder(const QString& qsid);
This method deletes a folder. id takes the ID of an existing folder.
This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)