pinwheel: Unpin nh from local nixpkgs to use cached builds

flake.nix

@@ -13,7 +13,6 @@
 
     nh = {
       url = "github:viperML/nh";
-      inputs.nixpkgs.follows = "nixpkgs";
     };
 
     nix-gc-env.url = "github:Julow/nix-gc-env";