refactor(nixos): inline module enable conditions

configs/nixos/modules/desktop/session/mako.nix

@@ -6,7 +6,6 @@
 }:
 # mako as the notification daemon: toasts, a do-not-disturb mode, and history recall.
 let
-  cfg = config.modules.desktop.session.mako; # NOLINT(let_order)
   user = config.user.name;
 
   makoctl = "${pkgs.mako}/bin/makoctl";
@@ -14,7 +13,7 @@ in
 {
   options.modules.desktop.session.mako.enable = lib.mkEnableOption "the mako notification daemon";
 
-  config = lib.mkIf cfg.enable {
+  config = lib.mkIf config.modules.desktop.session.mako.enable {
     home-manager.users.${user} = {
       # Colors and the popup font come from Stylix's mako target, so only
       # behaviour is set here.