Remove duplicate Managers field

It appears that the managers field was duplicated in the service root
response.

Tested: There was no change in the follow curl request
curl -c cjar -b cjar -k -H "Content-Type: application/json" -X GET https://192.168.7.2:443/redfish/v1/


{
  "@odata.id": "/redfish/v1",
  "@odata.type": "#ServiceRoot.v1_5_0.ServiceRoot",
  "AccountService": {
    "@odata.id": "/redfish/v1/AccountService"
  },
  "CertificateService": {
    "@odata.id": "/redfish/v1/CertificateService"
  },
  "Chassis": {
    "@odata.id": "/redfish/v1/Chassis"
  },
  "EventService": {
    "@odata.id": "/redfish/v1/EventService"
  },
  "Id": "RootService",
  "JsonSchemas": {
    "@odata.id": "/redfish/v1/JsonSchemas"
  },
  "Links": {
    "Sessions": {
      "@odata.id": "/redfish/v1/SessionService/Sessions"
    }
  },
  "Managers": {
    "@odata.id": "/redfish/v1/Managers"
  },
  "Name": "Root Service",
  "RedfishVersion": "1.9.0",
  "Registries": {
    "@odata.id": "/redfish/v1/Registries"
  },
  "SessionService": {
    "@odata.id": "/redfish/v1/SessionService"
  },
  "Systems": {
    "@odata.id": "/redfish/v1/Systems"
  },
  "Tasks": {
    "@odata.id": "/redfish/v1/TaskService"
  },
  "TelemetryService": {
    "@odata.id": "/redfish/v1/TelemetryService"
  },
  "UUID": "0d1ead49-71e5-47e2-943d-165635d7cf60",
  "UpdateService": {
    "@odata.id": "/redfish/v1/UpdateService"
  }
}

Signed-off-by: John Edward Broadbent <jebr@google.com>
Change-Id: Icc06d74fccf9efff6d36ef36559064dbab530ae6