Revert "[abacus15] add max walltime"

This reverts commit 9e3ef5ed.

data/grid5000/sites/rennes/clusters/abacus15/nodes/abacus15-1.json

@@ -278,7 +278,6 @@
   "supported_job_types": {
     "besteffort": true,
     "deploy": true,
-    "max_walltime": 604800,
     "queues": [
       "testing",
       "admin"

input/grid5000/sites/rennes/clusters/abacus15/abacus15.yaml

@@ -11,7 +11,6 @@ nodes:
     supported_job_types:
       deploy: true
       besteffort: true
-      max_walltime: 604800
     processor:
       microarchitecture: Zen 3
       clock_speed: 2650000000