This commit revues the Validate method from the Message interface as
the method is no longer used and is a relic from an older version of
the codebase.
This commit modifies the prior HTLCSettleRequest to more closely match
the UpdateFufillHTLC defined within the specification. The only
semantic change is the move from a slice of pre-images (for “multi-sig”
LN) to a single payment preimage.