Remove the usage of deprecated QApplication::setColorSpec()

This method has been deprecated and does not have any effect.

Task-number: QTBUG-76491
Change-Id: I001718cc48a2d8ba5caf81a66511814d2ff87ba4
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

examples/activeqt/opengl/main.cpp

@@ -78,7 +78,6 @@ QAXFACTORY_END()
 int main(int argc, char *argv[])
 {
     QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
-    QApplication::setColorSpec(QApplication::CustomColor);
     QApplication a(argc,argv);
 
     if (QOpenGLContext::openGLModuleType() != QOpenGLContext::LibGL) {