qfiledialog: clean up dead code.

Q_WS_WIN is never defined, and the qt_win_get_* functions don't exist
anymore. The QPA plugin takes care of doing the Windows-specific handling
for the file dialog.

Change-Id: Icdf9aed7da3db8ed2bd71d60f821869340ec1041
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
QFileDialog: compile with QT_NO_URL_CAST_FROM_STRING.

This is useful to detect confusions between local paths and URLs.

Change-Id: I1aa72ae10186984812691c8a1a4e843db3c85246
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>