[lille] remove elk and elk-dev

data/grid5000/sites/lille/servers/elk-dev.json

-{
-  "kind": "virtual",
-  "network_adapters": {
-    "default": {
-      "ip": "172.16.47.146"
-    }
-  },
-  "type": "server",
-  "uid": "elk-dev"
-}
\ No newline at end of file