We cleanup our output tracking for timeout txs when the peer's
htlc_timeout self-expiry is hit; we'd also log its spend if happen to
see it get spent.
This is a bit of a race as they can't spend it until the locktime is
available. Hence the flakiness in tests that expected the `htlc_timeout`
to *not* be spent.
Instead, we only log an external's `htlc_timeout` spend in the case
where we also immediately register another output to track for it (only
happens when said htlc is stealable)
Fixes#5405
In-Collab-With: @ddustin
f2e7e9d919