Refactor: `DELETE_INSTANCE_ID` under the `ServiceCert.CopperArgos.UseDeleteInstanceId`?

[mlajkim]

Background

Derived State for Service Cert is introduced in PR: #153

Seems like DELETE_INSTANCE_ID is part of CopperArgos (so basically there is a record for that instance id in Athenz db server) and we want to move that to the derived state.