Do not call CancelIo() in the AbstractOverlappedEventNotifier destructor

This function is used for "CreateFile" calls as opposed to "CreateEvent".
Hence, the usage has been erroneous in here.

See the MSDN links below for further details:

Overall: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363791%28v=vs.85%29.aspx

CreateFile: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858%28v=vs.85%29.aspx

CreateEvent: http://msdn.microsoft.com/en-us/library/windows/desktop/ms682396%28v=vs.85%29.aspx

It is also observed with a bit of testing that CancelIo() returns
ERROR_INVALID_HANDLE for some reason. This has not been tracked down though,
so it may be red-herring.

Change-Id: Ic2aea712763907dd9c9a32169702fa06308a7ee8
Reviewed-by: Laszlo Papp <lpapp@kde.org>