contractcourt: unify the lease specific HTLC sweeping logic

In this commit, we consolidate the _lease specific_ logic for the
success and timeout HTLC resolvers. We do this with the addition of a
new struct which is then composed via struct embedding with the two
existing structs. This fixes a flake in the integration tests by
ensuring the height is set up front, rather than eventually once the
height matches the lock time.

contractcourt/htlc_outgoing_contest_resolver.go

@@ -190,14 +190,6 @@ func (h *htlcOutgoingContestResolver) IsResolved() bool {
 	return h.resolved
 }
 
-// SupplementState allows the user of a ContractResolver to supplement it with
-// state required for the proper resolution of a contract.
-//
-// NOTE: Part of the ContractResolver interface.
-func (h *htlcOutgoingContestResolver) SupplementState(state *channeldb.OpenChannel) {
-	h.htlcTimeoutResolver.SupplementState(state)
-}
-
 // Encode writes an encoded version of the ContractResolver into the passed
 // Writer.
 //