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/ribbon/art.h

@@ -926,8 +926,7 @@ protected:
 
 #if defined(__WXMSW__)
 typedef wxRibbonMSWArtProvider wxRibbonDefaultArtProvider;
-#elif defined(__WXOSX_CARBON__) || \
-      defined(__WXOSX_COCOA__) || \
+#elif defined(__WXOSX_COCOA__) || \
       defined(__WXOSX_IPHONE__)
 // TODO: Once implemented, change typedef to OSX
 // typedef wxRibbonOSXArtProvider wxRibbonDefaultArtProvider;