Move TPraos logic from Ledger into Consensus

[amesgen]

For historical reasons, the logic for TPraos lives in Ledger instead of Consensus (which would be the natural place for the implementation of a ConsensusProtocol, as is already the case for eg PBft and Praos).

#340 already vendors one function (tickChainDepState) into Consensus, so it makes sense to also migrate the remaining logic.

[jorisdral]

I've looked through cardano-ledger, and only test packages currently depend on cardano-protocol-tpraos. However, it's probably still going to take a while to figure out how to completely decouple the TPraos logic from the ledger test code, and we possibly can't do it by ourselves (i.e., consensus team only)