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/toolbar.cpp

@@ -539,8 +539,6 @@ wxSize wxToolBar::DoGetBestSize() const
         sizeBest.y ++;
     }
 
-    CacheBestSize(sizeBest);
-
     return sizeBest;
 }