lnwallet: use signDesc.HashType for sweepsig in script_utils
lnwallet: use signDesc.HashType for sweepsig in script_utils

This commit changes the use of SigHash flags in the spend
transactions created in scrit_utils. Instead of always
using SigHashAll for the sweep signature, we instead use
the sighash flag specified by the passed sign descriptor.

LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd,LightningNetwork/lnd