Replace wxOVERRIDE and wxNOEXCEPT with override and noexcept

Don't use deprecated macros in wxWidgets itself.

samples/xrc/xrcdemo.h

@@ -34,7 +34,7 @@ public:
     // for the app initialization (doing it here and not in the ctor
     // allows to have an error return: if OnInit() returns false, the
     // application terminates)
-    virtual bool OnInit() wxOVERRIDE;
+    virtual bool OnInit() override;
 
 };