refactor(nixos): remove unused overlay

system/nixos/nixedo/configuration.nix

@@ -5,8 +5,6 @@
 { config, lib, pkgs, ... }:
 
 let
-  nixpkgs = import ../../shared/nixpkgs.nix { };
-
   configure-gtk = pkgs.writeTextFile {
     name = "configure-gtk";
     destination = "/bin/configure-gtk";
@@ -24,13 +22,17 @@ let
   };
 in
 {
-  nixpkgs = nixpkgs;
-
   imports = [
     # Include the results of the hardware scan.
     ./hardware-configuration.nix
   ];
 
+  nixpkgs = {
+    config = {
+      allowUnfree = true;
+    };
+  };
+
   # Bootloader.
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;

system/shared/nixpkgs.nix

@@ -1,5 +0,0 @@
-{}: {
-  config = { allowUnfree = true; };
-
-  overlays = [ (import ./overlays.nix) ];
-}

system/shared/overlays.nix

@@ -1 +0,0 @@
-self: super: { }