[flandres] Removed flandres from the repo.

Remove flandres from the repo, given the fact that this dom0 is not used anymore and getting erased of the production repo : see merge request on production repo.

Related to bug 13520.

data/grid5000/sites/lille/servers/flandres.json

-{
-  "alias": null,
-  "kind": "physical",
-  "network_adapters": {
-    "adm": {
-      "ip": "172.17.47.5",
-      "mac": "d4:ae:52:b0:e2:c7"
-    },
-    "bmc": {
-      "ip": "172.17.46.5",
-      "mac": "d4:ae:52:af:1c:71"
-    },
-    "default": {
-      "ip": "172.16.47.5",
-      "mac": "d4:ae:52:b0:e2:c6"
-    }
-  },
-  "pdu": [
-    {
-      "port": 3,
-      "uid": "pdu-b2p1"
-    },
-    {
-      "port": 3,
-      "uid": "pdu-b2p2"
-    }
-  ],
-  "serial": "9Q9WD5J",
-  "type": "server",
-  "uid": "flandres",
-  "warranty": "2019-07-28"
-}
\ No newline at end of file