[luxembourg] Remove nat-belval (replaced by nat)

data/grid5000/sites/luxembourg/servers/nat-belval.json

-{
-  "kind": "virtual",
-  "network_adapters": {
-    "default": {
-      "ip": "172.16.191.201"
-    }
-  },
-  "type": "server",
-  "uid": "nat-belval"
-}
\ No newline at end of file

input/grid5000/sites/luxembourg/servers/virtual.yaml

@@ -109,11 +109,6 @@ nat:
   network_adapters:
     default:
       ip: 172.16.191.200
-nat-belval:
-  kind: virtual
-  network_adapters:
-    default:
-      ip: 172.16.191.201
 oar:
   kind: virtual
   alias: