T2.1.1: Unnecessary double-commit in VoteData

[ggutoski]

Currently we are needlessly computing commitments of commitments in the impl of Committable for VoteData.

All variants of VoteData are of type Commitment<COMMITTABLE>. In other words: they are already commitments.

HotShot/crates/types/src/traits/election.rs

Lines 77 to 79 in 598b22e

	pub enum VoteData<COMMITTABLE: Committable + Serialize + Clone> {
	/// Vote to provide availability for a block.
	DA(Commitment<COMMITTABLE>),

However, the impl of Committable computes another commitment of the commitment:

HotShot/crates/types/src/traits/election.rs

Lines 95 to 102 in 598b22e

	impl<COMMITTABLE: Committable + Serialize + Clone> Committable for VoteData<COMMITTABLE> {
	fn commit(&self) -> Commitment<Self> {
	match self {
	VoteData::DA(block_commitment) => {
	commit::RawCommitmentBuilder::new("DA BlockPayload Commit")
	.field("block_commitment", *block_commitment)
	.finalize()
	}

Seems that VoteData should not impl Committable. Or, at the very least, its impl of Committable should just return the commitment that's already stored in VoteData.

[ggutoski]

I think we should remove the Committable impl.

A reasonable impl of Committable might look like this:

fn commit(&self) -> Commitment<Self> {
    match self {
        DA(c) | Yes(c) | No(c) | Timeout(c) | ViewSyncPreCommit(c) | ViewSyncCommit(c)
        | ViewSyncFinalize(c) => *c,
    }
}

However, the return type of the above code is Commitment<COMMITTABLE>. That might seem right, but any impl of Committable for VoteData<COMMITTABLE> must have return type Commitment<VoteData<COMMITTABLE>>. In other words, it must be a commitment of a commitment. We should not have anything with that type.