Replace xeon07 by hut in ssh config

The xeon07 machine has been renamed to hut.

Reviewed-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

m/module/ssh-hut-extern.nix

@@ -1,9 +1,8 @@
 {
   programs.ssh.extraConfig = ''
-    Host ssfhead
+    Host apex ssfhead
       HostName ssflogin.bsc.es
     Host hut
-      ProxyJump ssfhead
-      HostName xeon07
+      ProxyJump apex
   '';
 }