Can Ouroboros.Consensus.Storage.ChainDB.Impl.Follower be simplified via its private registry

After Issue input-output-hk/ouroboros-network#2892, the combinator that provides a private registry will be used to allocate `Follower`. Can the `Follower` implementation rely on the privateness of the registry in order to offload some of the tracking its doing to the registry? Basic idea: when we close the Follower, it can close its private registry.