fix(hosts/orion): use default nix version

Problem: Latest versions of `nix` seem to segfault on flake updates
Solution: Use a known stable version of `nix`

hosts/orion/modules/nix.nix

@@ -1,9 +1,8 @@
-{ inputs, pkgs, ... }:
+{ inputs, ... }:
 
 {
   nixpkgs.config.allowUnfree = true;
   nix = {
-    package = pkgs.nixVersions.latest;
     nixPath = [ "nixpkgs=${inputs.nixpkgs}" ];
     settings = {
       experimental-features = [
@@ -29,4 +28,4 @@
       options = "--delete-older-than 7d";
     };
   };
-}
+}