refactor(grfn): Stop importing nixpkgs a bunch of times

Once is enough!

<grfn> https://tazj.in/blobs/touch-garbage.jpg

Change-Id: I68f66669e82d35a71752638450fa4b820e137172
Signed-Off-By: Florian Klink <flokli@flokli.de>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3048
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

users/grfn/system/system/modules/common.nix

@@ -56,8 +56,6 @@ with lib;
     shell = pkgs.zsh;
   };
 
-  nixpkgs.config.allowUnfree = true;
-
   nix = {
     trustedUsers = [ "grfn" ];
     autoOptimiseStore = true;

users/grfn/system/system/modules/sound.nix

@@ -1,9 +1,9 @@
 { config, lib, pkgs, ... }:
+
 {
   # Enable sound.
   sound.enable = true;
   hardware.pulseaudio.enable = true;
-  nixpkgs.config.pulseaudio = true;
 
   environment.systemPackages = with pkgs; [
     pulseaudio-ctl