networking: stop configuring NIS domain name

The `domainname` utility uses setdomainname (see getdomainname(2)) to
configure the NIS[1] (also known as YP) domain name.

It provided a central directory for various objects that are resolved via
nsswitch in the late 1990s and early 2000s.

It is however not a safe nor common deployment scenario anymore.

[1] https://en.wikipedia.org/wiki/Network_Information_Service

nixos/modules/tasks/network-interfaces.nix

@@ -1617,18 +1617,6 @@ in
         )
       );
 
-    systemd.services.domainname = lib.mkIf (cfg.domain != null) {
-      wantedBy = [ "sysinit.target" ];
-      before = [
-        "sysinit.target"
-        "shutdown.target"
-      ];
-      conflicts = [ "shutdown.target" ];
-      unitConfig.DefaultDependencies = false;
-      serviceConfig.ExecStart = ''${pkgs.nettools}/bin/domainname "${cfg.domain}"'';
-      serviceConfig.Type = "oneshot";
-    };
-
     environment.etc.hostid = mkIf (cfg.hostId != null) { source = hostidFile; };
     boot.initrd.systemd.contents."/etc/hostid" = mkIf (cfg.hostId != null) { source = hostidFile; };