Avoid ifdef-ed override specification

Instead, add the base class functions so the derived class always
overrides. If/when wxX11 and wxMotif are removed there won't be an
ifdef that no one ever notices isn't needed anymore.

include/wx/unix/glx11.h

@@ -146,10 +146,7 @@ public:
     // This method is not currently used by the library itself, but remains for
     // backwards compatibility and also because wxGTK has it we could start
     // using it for the same purpose in wxX11 too some day.
-    virtual void *GetXVisualInfo()
-#ifdef __WXGTK20__
-                                    wxOVERRIDE
-#endif
+    virtual void* GetXVisualInfo() wxOVERRIDE
     {
         return wxGLCanvasX11::GetDefaultXVisualInfo();
     }