refactor: Remove manual high-dpi support

This removes the --scale command line option.
Qt6 seems to have this already integrated to scale according to the
nativ display settings: https://doc.qt.io/qt-6.8/highdpi.html
Adjusting the scale on a per-application basis is not intended (anymore)
according to the documentation.
Tested on a (near) high-dpi screen.

samples/hotkey/main.cpp

@@ -16,7 +16,6 @@ using namespace swift::gui;
 //! main
 int main(int argc, char *argv[])
 {
-    CGuiApplication::highDpiScreenSupport();
     QApplication qa(argc, argv);
     CGuiApplication a("samplehotkey", swift::misc::CApplicationInfo::Sample, QPixmap());
     swift::gui::components::CSettingsHotkeyComponent w;