Avoid a `short_to_chan_info` read lock in `claim_funds_from_hop`

Avoid a `short_to_chan_info` read lock in `claim_funds_from_hop`

In 453ed11f80b40f28b6e95a74b1f7ed2cd7f012ad we started tracking the
counterparty's `node_id` in `HTLCPreviousHopData`, however we were
still trying to look it up using `prev_short_channel_id` in
`claim_funds_from_hop`.

Because we now usually have the counterparty's `node_id` directly
accessible, we should skip the `prev_short_channel_id` lookup.

This will also be more important in the next commit where we need
to look up state for our counterparty to generate
`ChannelMonitorUpdate`s whether we have a live channel or not.