nix: don't use nix flake

I originally wanted to use the nix flake to allow users to take
advantage of the latest changes. Just so happened that nixpkgs was
recently updated with a new version around the same time, and this
just adds complexity for no real gain.

Author: nrdxp

extern/default.nix

@@ -9,7 +9,6 @@ in
   ];
 
   overlays = [
-    nix.overlay
     nur.overlay
     devshell.overlay
     (final: prev: {

flake.lock

@@ -22,14 +22,13 @@
       home.inputs.nixpkgs.follows = "nixos";
       naersk.url = "github:nmattia/naersk";
       naersk.inputs.nixpkgs.follows = "override";
-      nix.inputs.nixpkgs.follows = "nixos";
       nixos-hardware.url = "github:nixos/nixos-hardware";
       utils.url = "github:numtide/flake-utils/flatten-tree-system";
       pkgs.url = "path:./pkgs";
       pkgs.inputs.nixpkgs.follows = "nixos";
     };
 
-  outputs = inputs@{ deploy, nixos, nur, nix, self, utils, ... }:
+  outputs = inputs@{ deploy, nixos, nur, self, utils, ... }:
     let
       inherit (self) lib;
       inherit (lib) os;