refactor(nixos): inline module enable conditions

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

@@ -6,13 +6,12 @@
 # tmux for the primary user, configured through home-manager.
 # Settings without a home-manager option are read from ./extra.conf.
 let
-  cfg = config.modules.shell.tmux; # NOLINT(let_order)
   user = config.user.name;
 in
 {
   options.modules.shell.tmux.enable = lib.mkEnableOption "tmux, configured via home-manager";
 
-  config = lib.mkIf cfg.enable {
+  config = lib.mkIf config.modules.shell.tmux.enable {
     registry.shell-shortcut.${config.networking.hostName}.tmx = "tmux new-session -A -s";
 
     home-manager.users.${user}.programs.tmux = {