chain: continue to accept []wire.OutPoint for rescan updates for bitcoind
chain: continue to accept []wire.OutPoint for rescan updates for bitcoind

In this commit, we fix a recently introduced bug that would cause
callers that attempted to get a spend notifications for a particular
outpoint to no longer get that precise notification. In a prior commit,
in preparation for the new neutrino gcs filter format, we added a
mapping from script to outpoint that will be used by neutrino, and later
other backends as well. However, we still need to match on outpoint
slices for bitcoind today.

btcsuite/btcwallet,btcsuite/btcwallet