Remove noop modification of QDialogPrivate::nativeDialogInUse

The modification was inside a nativeDialogInUse == false
condition already.

Task-number: QTBUG-108153
Change-Id: Ice5f48fc5d2548085b063060817e2c4eeaf00452
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/dialogs/qfontdialog.cpp

@@ -970,7 +970,6 @@ void QFontDialog::setVisible(bool visible)
         // updates the state correctly, but skips showing the non-native version:
         setAttribute(Qt::WA_DontShowOnScreen, true);
     } else {
-        d->nativeDialogInUse = false;
         setAttribute(Qt::WA_DontShowOnScreen, false);
     }
     QDialog::setVisible(visible);