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/generic/treectlg.cpp

@@ -4153,9 +4153,6 @@ wxSize wxGenericTreeCtrl::DoGetBestSize() const
     if ( dy )
         size.y += PIXELS_PER_UNIT - dy;
 
-    // we need to update the cache too as the base class cached its own value
-    CacheBestSize(size);
-
     return size;
 }