refactor(nixos): inline module enable conditions

configs/nixos/modules/desktop/utilities/userdirs.nix

@@ -2,13 +2,12 @@
 # Declares the XDG user directories, so a tool that queries them lands in a
 # well-known folder a host can relocate from one place.
 let
-  cfg = config.modules.desktop.utilities.userdirs; # NOLINT(let_order)
   user = config.user.name;
 in
 {
   options.modules.desktop.utilities.userdirs.enable = lib.mkEnableOption "XDG user directories";
 
-  config = lib.mkIf cfg.enable {
+  config = lib.mkIf config.modules.desktop.utilities.userdirs.enable {
     # Write ~/.config/user-dirs.dirs from the option defaults.
     home-manager.users.${user}.xdg.userDirs.enable = true;
   };