Remove wxMenuItem::GetBitmapBundle() from wxGTK

This function doesn't exist in the other ports and is not really needed
in this one neither, so just remove it for now.

If we really want to have it, we need to make it available everywhere.

src/gtk/menu.cpp

@@ -1034,7 +1034,7 @@ void wxMenu::GtkAppend(wxMenuItem* mitem, int pos)
             menuItem = gtk_menu_item_new_with_label("");
 #else
             wxGCC_WARNING_SUPPRESS(deprecated-declarations)
-            if (mitem->GetBitmapBundle().IsOk())
+            if (mitem->GetBitmap().IsOk())
             {
                 menuItem = gtk_image_menu_item_new_with_label("");
             }