nix config: misc tidying

Let's be real, I am doing this because I got impatient with the
gratuitous copy to the store this eliminates caused by pkgs.path.

Also gets rid of stuff in nix.extraOptions which is deprecated.

configurations.nix

@@ -60,7 +60,7 @@ let
       {
         nix.nixPath = [
           "home-manager=${home-manager}"
-          "nixpkgs=${pkgs.path}"
+          "nixpkgs=flake:nixpkgs"
           "nur=${nur}"
         ];
         # TODO: share nixpkgs for each machine to speed up local evaluation.
@@ -72,10 +72,7 @@ let
         #};
         # sops.defaultSopsFile = lib.mkIf (builtins.pathExists sopsFile) sopsFile;
 
-        nix.extraOptions = ''
-          flake-registry = ${flake-registry}/flake-registry.json
-          builders-use-substitutes = true
-        '';
+        nix.settings.builders-use-substitutes = true;
 
         nix.registry = {
           home-manager.flake = home-manager;

flake.lock

@@ -199,22 +199,6 @@
         "type": "github"
       }
     },
-    "flake-registry": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1717415742,
-        "narHash": "sha256-HKvoLGZUsBpjkxWkdtctGYj6RH0bl6vcw0OjTOqyzJk=",
-        "owner": "NixOS",
-        "repo": "flake-registry",
-        "rev": "895a65f8d5acf848136ee8fe8e8f736f0d27df96",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "flake-registry",
-        "type": "github"
-      }
-    },
     "flake-utils": {
       "locked": {
         "lastModified": 1667395993,
@@ -502,7 +486,6 @@
         "colmena": "colmena",
         "disko": "disko",
         "flake-parts": "flake-parts",
-        "flake-registry": "flake-registry",
         "home-manager": "home-manager_2",
         "lix": "lix",
         "lix-module": "lix-module",

flake.nix

@@ -41,9 +41,6 @@
     # Private repository, you need a valid SSH key to access it
     # nixos-hypervisor.url = "git+ssh://gitea@git.newtype.fr/newtype/nixos-hypervisor?ref=main";
     # nixos-hypervisor.inputs.nixpkgs.follows = "nixpkgs";
-
-    flake-registry.url = "github:NixOS/flake-registry";
-    flake-registry.flake = false;
   };
 
   outputs =