refactor(nixos): inline module enable conditions

configs/nixos/modules/shell/direnv/default.nix

@@ -5,14 +5,13 @@
 }:
 # direnv for the primary user, configured through home-manager.
 let
-  cfg = config.modules.shell.direnv; # NOLINT(let_order)
   user = config.user.name;
 in
 {
   options.modules.shell.direnv.enable =
     lib.mkEnableOption "direnv for the primary user, with nix-direnv shell caching";
 
-  config = lib.mkIf cfg.enable {
+  config = lib.mkIf config.modules.shell.direnv.enable {
     home-manager.users.${user}.programs.direnv = {
       enable = true;
       silent = true;