Add common implementations of wxStaticBitmap icon methods

Instead of defining them, slightly differently, in all the non-MSW
ports, define them once in wxStaticBitmapBase.

No real changes, this is just a simplification.

include/wx/generic/statbmpg.h

@@ -44,18 +44,6 @@ public:
 
     virtual wxBitmap GetBitmap() const wxOVERRIDE { return m_bitmap; }
 
-    virtual void SetIcon(const wxIcon& icon) wxOVERRIDE
-    {
-        m_bitmap.CopyFromIcon(icon);
-        SetInitialSize(GetBitmapSize());
-        Refresh();
-    }
-
-#if defined(__WXGTK20__) || defined(__WXMAC__)
-    // icons and bitmaps are really the same thing in wxGTK and wxMac
-    wxIcon GetIcon() const wxOVERRIDE  { return (const wxIcon &)m_bitmap; }
-#endif
-
     virtual void SetScaleMode(ScaleMode scaleMode) wxOVERRIDE
     {
         m_scaleMode = scaleMode;