nixos: move left-behind allowUnfree comment

nixos/lib/eval-config.nix

@@ -54,11 +54,6 @@ in rec {
 
   # These are the extra arguments passed to every module.  In
   # particular, Nixpkgs is passed through the "pkgs" argument.
-  # FIXME: we enable config.allowUnfree to make packages like
-  # nvidia-x11 available. This isn't a problem because if the user has
-  # ‘nixpkgs.config.allowUnfree = false’, then evaluation will fail on
-  # the 64-bit package anyway. However, it would be cleaner to respect
-  # nixpkgs.config here.
   extraArgs = extraArgs_ // {
     inherit modules baseModules;
   };