remove nix registry if nix is disabled

modules/nix/link-inputs.nix

@@ -1,19 +1,22 @@
 {
   lib,
-  inputs,
+  pureInputs,
+  config,
   ...
 }:
 let
   # Taken from https://github.com/gytis-ivaskevicius/flake-utils-plus/blob/master/lib/options.nix
   inherit (lib) filterAttrs mapAttrs';
-  flakes = filterAttrs (name: value: (value ? outputs)) inputs;
+  flakes = filterAttrs (
+    name: value: (value ? outputs) && (name != "self") && (name != "nixos-config")
+  ) pureInputs;
   nixRegistry = builtins.mapAttrs (name: v: { flake = v; }) flakes;
 in
 {
   nix.registry = nixRegistry;
   environment.etc = mapAttrs' (name: value: {
     name = "nix/inputs/${name}";
-    value = {
+    value = lib.mkIf config.nix.enable {
       source = value.outPath;
     };
   }) flakes;