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/osx/listbox.h

@@ -167,10 +167,6 @@ protected:
     wxArrayPtrVoid m_itemsClientData;
 
 private:
-#ifdef __WXOSX_CARBON__
-    // It needs to call our CalcAndSendEvent().
-    friend class wxMacDataBrowserListControl;
-#endif // Carbon
 
     wxDECLARE_DYNAMIC_CLASS(wxListBox);
     wxDECLARE_EVENT_TABLE();