remove cluster_name from relation data

Slurmdbd should no longer depends on slurmctld. The cluster_name,
used for tagging the associated cluster in the fluentbit config
is not necessary and can be removed to enable independent operation.

src/interface_slurmdbd.py

@@ -84,7 +84,6 @@ def _on_relation_created(self, event: RelationCreatedEvent) -> None:
                 {
                     "munge_key": self._charm.get_munge_key(),
                     "jwt_rsa": self._charm.get_jwt_rsa(),
-                    "cluster_name": self._charm.cluster_name,
                 }
             )
         except json.JSONDecodeError as e: