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/Mod/Mesh/Gui/SoFCIndexedFaceSet.cpp

@@ -414,7 +414,7 @@ bool MeshRenderer::matchMaterial(SoState* state) const
 bool MeshRenderer::shouldRenderDirectly(bool direct)
 {
 #ifdef RENDER_GL_VAO
-    Q_UNUSED(direct);
+    (void)direct;
     return false;
 #else
     return direct;
@@ -754,7 +754,7 @@ void SoFCIndexedFaceSet::generateGLArrays(SoGLRenderAction* action)
         numcolors = gl->getNumDiffuse();
         transp = gl->getTransparencyPointer();
         numtransp = gl->getNumTransparencies();
-        Q_UNUSED(numtransp);
+        (void)numtransp;
     }
 
     std::vector<float> face_vertices;

src/Mod/Sandbox/Gui/Overlay.cpp

@@ -47,7 +47,7 @@ using namespace SandboxGui;
 
 class MyPaintable : public Gui::GLGraphicsItem
 {
-    QtGLFramebufferObject* fbo;
+    QOpenGLFramebufferObject* fbo;
     Gui::View3DInventorViewer* view;
     QImage img;
 public:
@@ -63,7 +63,7 @@ public:
             p.drawText(200,200,QStringLiteral("Render to QImage"));
         }
 
-        fbo = new QtGLFramebufferObject(v->getGLWidget()->size());
+        fbo = new QOpenGLFramebufferObject(v->getGLWidget()->size());
         fbo->bind();
         fbo->release();
 
@@ -92,7 +92,7 @@ public:
 
 class Teapots : public Gui::GLGraphicsItem
 {
-    QtGLFramebufferObject *fbObject;
+    QOpenGLFramebufferObject *fbObject;
     GLuint glTeapotObject;
     QPoint rubberBandCorner1;
     QPoint rubberBandCorner2;
@@ -106,8 +106,8 @@ Teapots(Gui::View3DInventorViewer* v) :view(v)
     SbVec2s size = vp.getViewportSizePixels();
 
     rubberBandIsShown = false;
-    fbObject = new QtGLFramebufferObject(size[0],size[1],
-                                         QtGLFramebufferObject::Depth);
+    fbObject = new QOpenGLFramebufferObject(size[0],size[1],
+                                         QOpenGLFramebufferObject::Depth);
     resizeGL(size[0],size[1]);
 
     rubberBandIsShown = true;
@@ -332,7 +332,7 @@ DrawingPlane::~DrawingPlane()
 
 void DrawingPlane::initialize()
 {
-    fbo = new QtGLFramebufferObject(128, 128,QtGLFramebufferObject::Depth);
+    fbo = new QOpenGLFramebufferObject(128, 128,QOpenGLFramebufferObject::Depth);
 }
 
 void DrawingPlane::terminate()
@@ -353,7 +353,7 @@ void DrawingPlane::draw ()
 {return;
     if (1/*mustRedraw*/) {
         SbVec2s view = _pcView3D->getSoRenderManager()->getSize();
-        static_cast<QtGLWidget*>(_pcView3D->getGLWidget())->makeCurrent();
+        static_cast<QOpenGLWidget*>(_pcView3D->getGLWidget())->makeCurrent();
     glMatrixMode(GL_PROJECTION);
     glPushMatrix();
     glLoadIdentity();

src/Mod/Sandbox/Gui/Overlay.h

@@ -55,7 +55,7 @@ private:
     QPoint lastPoint;
     QList<QPoint> selection;
 
-    QtGLFramebufferObject* fbo;
+    QOpenGLFramebufferObject* fbo;
 };
 
 } // SandboxGui