Revert "[rennes][abacus15] Add new cluster"

This reverts commit 04a32ef1.

data/grid5000/sites/rennes/clusters/abacus15/abacus15.json

-{
-  "boot_type": "uefi",
-  "created_at": "Mon, 09 Oct 2023 00:00:00 GMT",
-  "exotic": false,
-  "kavlan": false,
-  "metrics": [
-
-  ],
-  "model": "DELL C4140",
-  "queues": [
-    "production",
-    "admin"
-  ],
-  "type": "cluster",
-  "uid": "abacus15"
-}
\ No newline at end of file

input/grid5000/ipv4.yaml

@@ -71,7 +71,6 @@ ipv4:
       rennes parasilo eth1 0 0 1 100
       rennes abacus20 eth0 0 0 13 19
       rennes abacus25 eth0 0 0 13 24
-      rennes abacus15 eth0 0 0 13 14
       rennes roazhon4 eth0 0 0 14 3
       sophia uvb eth0 0 0 4 0
       toulouse montcalm eth0 0 0 8 0