Remove wxOSX/Carbon support.

Cocoa has been the default toolkit in wxWidgets for a long time. There is really no good reason to use Carbon in 2016 and this removes a lot of unused and unmaintained code.

include/wx/mediactrl.h

@@ -218,13 +218,6 @@ protected:
     virtual void DoMoveWindow(int x, int y, int w, int h) wxOVERRIDE;
     wxSize DoGetBestSize() const wxOVERRIDE;
 
-    //FIXME:  This is nasty... find a better way to work around
-    //inheritance issues
-#if defined(__WXOSX_CARBON__)
-    virtual void MacVisibilityChanged();
-
-    friend class wxQTMediaBackend;
-#endif
     class wxMediaBackend* m_imp;
     bool m_bLoaded;