Gui: Cleanup Qt OpenGL usings in QtOpenGL.h.

Previously the code defined compatiblity usings in `QtOpenGL.h` header,
which I think was added for backwards compatiblity with previous Qt
OpenGL widgets.

As far as I can tell, this is not necessary anymore, and can be cleaned
up.

src/Gui/SplitView3DInventor.cpp

@@ -580,7 +580,7 @@ SplitView3DInventor::SplitView3DInventor(int views, Gui::Document* pcDocument, Q
     bool smoothing = false;
     bool glformat = false;
     int samples = View3DInventorViewer::getNumSamples();
-    QtGLFormat f;
+    QSurfaceFormat f;
 
     if (samples > 1) {
         glformat = true;