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/core/private/datetimectrl.h

@@ -29,8 +29,6 @@ enum wxDateTimeWidgetKind
 class wxDateTimeWidgetImpl
 #if wxOSX_USE_COCOA
     : public wxWidgetCocoaImpl
-#elif wxOSX_USE_CARBON
-    : public wxMacControl
 #else
     #error "Unsupported platform"
 #endif
@@ -58,10 +56,6 @@ protected:
         : wxWidgetCocoaImpl(wxpeer, view)
     {
     }
-#elif wxOSX_USE_CARBON
-    // There is no Carbon implementation of this control yet so we don't need
-    // any ctor for it yet but it should be added here if Carbon version is
-    // written later.
 #endif
 };