let me upgrade walls with exilar again

I personally like having the choice to upgrade my walls with exilar or gold. Im trying to max a th 8 right now so I simply can't upgrade my walls because I need gold for other stuff. Upgrading walls with exilar finally let me work on my walls at the same time. So it would be nice to have that feature back

I'm not sure that SC intended for players to max their walls and at least no elixir walls at TH8 means that you can rob TH8s easier when you become TH9