lnwallet: update the witness generation funcs for sender's HTLC output
lnwallet: update the witness generation funcs for sender's HTLC output

This commit updates all the spendHtlcSpend* functions which are used to
spend each of the possible clauses within the HTLC contract placed on
the sender’s commitment transaction.

LightningNetwork/lnd,aakselrod/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,AndrewSamokhvalov/lnd,aakselrod/lnd,ddustin/lnd,LightningNetwork/lnd