SignableMsg consensus step is hardcoded to "6"

[tarcieri]

The KMS needs to know the correct round step of the consensus state for double signing detection:

https://github.com/interchainio/tendermint-rs/blob/566dfb6/src/amino_types/vote.rs#L170

See this PR for how the KMS is parsing it:

tendermint/tmkms#348

[zmanian]

A little bit of where I've been stuck on fixing it is that there seems to be some inconsistency in the code base about what consensus states map to a given step.

I've seen propose 0, prevote 1 and preccommit 2.

I've also seen propose 0, prevote 2, preccommit 3.

[tarcieri]

There's this mapping, where PreVote is 4 and PreCommit is 6 (ostensibly where the hardcoded 6 comes from):

https://github.com/tendermint/tendermint/blob/f39138aa2e543438548a150bdad45304ccc3296b/consensus/types/round_state.go#L18

There's also this mapping which is already in tendermint-rs:

https://github.com/interchainio/tendermint-rs/blob/566dfb6/src/amino_types/signature.rs#L40

    match self {
        // Votes
        SignedMsgType::PreVote => 0x01,
        SignedMsgType::PreCommit => 0x02,
        // Proposals
        SignedMsgType::Proposal => 0x20,
    }

The one I used in this PR was suggested by @ebuchman:

https://github.com/tendermint/kms/pull/348/files#diff-4c9ae8d0d599659f5476e14edb82cbaeR250

   match msg_type {
        SignedMsgType::Proposal => 0,
        SignedMsgType::PreVote => 1,
        SignedMsgType::PreCommit => 2,
    }

I think it really doesn't matter too much so long as it moves Propose -> PreVote -> PreCommit and the step increments between each, and moving between a block ID and <nil> is allowed between steps.

[thanethomson]

Is this still relevant? The code on master at the moment seems like it's deprecated: https://github.com/informalsystems/tendermint-rs/blob/master/tendermint/src/vote.rs#L148

[tarcieri]

KMS isn't seeing any deprecation warnings, so I think this can be safely removed?