Remove the DataAvailabilityHeader from the Proposal

[evan-forbes]

Summary

We no longer need the DataAvailaibiltyHeader in the Proposal, so we should remove it.

Details

Originally introduced in #248, the DAH was added to the Proposal so that validators could sample and verify fraud proofs during consensus. That is no longer necessary, so it should be removed. Removal might be a tad cumbersome, as we've made quite a few changes since #248, so if doing a simple git revert causes a lot a issues, we can remove it manually.

Since the DAH will no longer be in the proposal or the block #512 , we should keep the DAH in BlockMeta as to still save it, or save it separately.

Action Items

• Remove the DataAvailabilityHeader from the Proposal

References

comment that spawned the discussion.
tracked in #491 and #506