Don't emit autoLogin config with eval warning

Fix this evaluation warning on the first rebuild after install:

  [test@nixos:~]$ sudo nixos-rebuild build
  building Nix...
  building the system configuration...
  evaluation warning: The option `services.xserver.displayManager.autoLogin' defined in `/etc/nixos/configuration.nix' has been renamed to `services.displayManager.autoLogin'.

modules/nixos/main.py

@@ -277,8 +277,8 @@
 """
 
 cfgautologin = """  # Enable automatic login for the user.
-  services.xserver.displayManager.autoLogin.enable = true;
-  services.xserver.displayManager.autoLogin.user = "@@username@@";
+  services.displayManager.autoLogin.enable = true;
+  services.displayManager.autoLogin.user = "@@username@@";
 
 """