Don't call CacheBestSize() from DoGetBestSize() implementations

This is unnecessary, wxWindow::GetBestSize() already does this, so calling it
from DoGetBestSize() called by it too is just useless.

src/msw/statusbar.cpp

@@ -497,9 +497,7 @@ wxSize wxStatusBar::DoGetBestSize() const
     int height = GetCharHeight();
     height += 4*borders.vert;
 
-    wxSize best(width, height);
-    CacheBestSize(best);
-    return best;
+    return wxSize(width, height);
 }
 
 void wxStatusBar::DoMoveWindow(int x, int y, int width, int height)