remove configuration.nix

it's no longer needed in nixos-22.05

configuration.nix

@@ -1,24 +0,0 @@
-# Edit this configuration file to define what should be installed on
-# your system.  Help is available in the configuration.nix(5) man page
-# and in the NixOS manual (accessible by running ‘nixos-help’).
-
-# USEFUL COMMANDS:
-#   nix show-config
-#   nix eval --raw <expr>  => print an expression. e.g. nixpkgs.raspberrypifw prints store path to the package
-#   nix-option   ##  query options -- including their SET VALUE; similar to search: https://search.nixos.org/options
-#   nixos-rebuild switch --upgrade   ## pull changes from the nixos channel (e.g. security updates) and rebuild
-
-{ pkgs, ... }:
-
-{
-  # enable flake support.
-  # the real config root lives in flake.nix
-  nix = {
-    #package = pkgs.nixFlakes;
-    package = pkgs.nixUnstable;
-    extraOptions = ''
-      experimental-features = nix-command flakes
-    '';
-  };
-}
-

flake.nix

@@ -67,7 +67,6 @@
         inherit system;
         specialArgs = { inherit home-manager nurpkgs; };
         modules = [
-          ./configuration.nix
           ./modules
           ./machines/${name}
           (import ./helpers/set-hostname.nix name)
@@ -117,6 +116,7 @@
 
           # stable telegram doesn't build, so explicitly use the stable one.
           # TODO: apply this specifically to the moby build?
+          # TODO: all systems are using stable nixos. remove this?
           # tdesktop = pkgs-telegram.legacyPackages.${system}.tdesktop;
           tdesktop = nixpkgs.legacyPackages.${system}.tdesktop;
 

modules/universal/home-manager.nix

@@ -223,7 +223,6 @@ in
         pkgs.netcat
         pkgs.networkmanager
         pkgs.nixpkgs-review
-        pkgs.nixUnstable  # TODO: still needed on 22.05?
         # pkgs.nixos-generators
         # pkgs.nettools
         pkgs.nmap