migrate to nix flake

systems/LoutreOS/configuration.nix

@@ -4,10 +4,6 @@
 
 { config, pkgs, ... }:
 
-let
-  gitRev = "4c45e960e797d660358a11723e736afee3998261";
-  nixpkgs = fetchTarball "https://github.com/nyanloutre/nixpkgs/archive/${gitRev}.tar.gz";
-in
 {
   imports = [
     ../common-cli.nix
@@ -27,10 +23,12 @@ in
     tmpOnTmpfs = true;
   };
 
-  nix.nixPath = [
-    "nixpkgs=${nixpkgs}"
-    "nixos-config=/etc/nixos/configuration.nix"
-  ];
+  nix = {
+    package = pkgs.nixUnstable;
+    extraOptions = ''
+      experimental-features = nix-command flakes
+    '';
+  };
 
   documentation.nixos.enable = false;