screen: move pam service to module

nixos/modules/programs/screen.nix

@@ -27,6 +27,7 @@ in
     environment.etc.screenrc.text = cfg.screenrc;
 
     environment.systemPackages = [ pkgs.screen ];
+    security.pam.services.screen = {};
   };
 
 }

nixos/modules/security/pam.nix

@@ -781,7 +781,6 @@ in
         ftp = {};
         i3lock = {};
         i3lock-color = {};
-        screen = {};
         vlock = {};
         xlock = {};
         xscreensaver = {};