Move GetBitmapFromBundle() to wxMenuItemBase

This is just a refactoring to avoid duplicating this function code in
all ports and just have it once in the base class.

include/wx/msw/menuitem.h

@@ -15,8 +15,6 @@
 // headers
 // ----------------------------------------------------------------------------
 
-#include "wx/bmpbndl.h"
-
 #if wxUSE_OWNER_DRAWN
     #include "wx/ownerdrw.h"
 
@@ -134,8 +132,6 @@ private:
     // common part of all ctors
     void Init();
 
-    wxBitmap GetBitmapFromBundle(const wxBitmapBundle& bundle) const;
-
     // Return the item position in the menu containing it.
     //
     // Returns -1 if the item is not attached to a menu or if we can't find its