This:

• removes errors that are meant for the client since these can live in the drand/go-clients repo now.
• removes the Bolt Option since we never used these and twiddling with the bolt DB can be a bit risk for the Sync and all, simplifies the Config.
• removing the now internal but unused WithinTran function which I think was never used anywhere, not even in our DB migration tool?
• removing the ByKey struct meant to order nodes in the group file since ordering is now handled by the DKG code.