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/SoFCOffscreenRenderer.cpp

@@ -563,9 +563,9 @@ SoQtOffscreenRenderer::makeFrameBuffer(int width, int height, int samples)
 
     viewport.setWindowSize(width, height);
 
-    QtGLFramebufferObjectFormat fmt;
+    QOpenGLFramebufferObjectFormat fmt;
     fmt.setSamples(samples);
-    fmt.setAttachment(QtGLFramebufferObject::Depth);
+    fmt.setAttachment(QOpenGLFramebufferObject::Depth);
     // With enabled alpha a transparent background is supported but
     // at the same time breaks semi-transparent models. A workaround
     // is to use a certain background color using GL_RGB as texture
@@ -573,7 +573,7 @@ SoQtOffscreenRenderer::makeFrameBuffer(int width, int height, int samples)
     // replaces it with the color requested by the user.
     fmt.setInternalTextureFormat(this->texFormat);
 
-    framebuffer = new QtGLFramebufferObject(width, height, fmt);
+    framebuffer = new QOpenGLFramebufferObject(width, height, fmt);
     cache_context = SoGLCacheContextElement::getUniqueCacheContext(); // unique per pixel buffer object, just to be sure
 }