remove deprecated system passing

fixes
'system' has been renamed to/replaced by 'stdenv.hostPlatform.system'

Wherever possible, it's best to reference the hostPlatform of the
nixpkgs instance directly via `config`. This is only possible in NixOS
systems though, for standalon home-manager configs we need to get that
value through `pkgs.stdenv`.

common/guest.nix

@@ -1,7 +1,6 @@
 {
   config,
   lib,
-  system,
   ...
 }:
 let
@@ -56,7 +55,7 @@ in
         # Optionally use extraSpecialArgs
         # to pass through arguments to home.nix
         extraSpecialArgs = {
-          inherit inputs system;
+          inherit inputs;
         };
 
       };