Remove unused bwc variable from ApiKeyService (elastic#81964)

* Remove unused bwc variable from ApiKeyService

The variable lives in Subject since elastic#80926.

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ApiKeyService.java

@@ -200,45 +200,6 @@ public class ApiKeyService {
         Property.NodeScope
     );
 
-    // This following fixed role descriptor is for fleet-server BWC on and before 7.14.
-    // It is fixed and must NOT be updated when the fleet-server service account updates.
-    private static final BytesArray FLEET_SERVER_ROLE_DESCRIPTOR_BYTES_V_7_14 = new BytesArray("""
-        {
-          "elastic/fleet-server": {
-            "cluster": [ "monitor", "manage_own_api_key" ],
-            "indices": [
-              {
-                "names": [
-                  "logs-*",
-                  "metrics-*",
-                  "traces-*",
-                  "synthetics-*",
-                  ".logs-endpoint.diagnostic.collection-*"
-                ],
-                "privileges": [ "write", "create_index", "auto_configure" ],
-                "allow_restricted_indices": false
-              },
-              {
-                "names": [ ".fleet-*" ],
-                "privileges": [
-                  "read",
-                  "write",
-                  "monitor",
-                  "create_index",
-                  "auto_configure"
-                ],
-                "allow_restricted_indices": false
-              }
-            ],
-            "applications": [],
-            "run_as": [],
-            "metadata": {},
-            "transient_metadata": {
-              "enabled": true
-            }
-          }
-        }""");
-
     private final Clock clock;
     private final Client client;
     private final SecurityIndexManager securityIndex;