coin-moves: only log htlc_timeout pair for penalty txs

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

tests/test_closing.py

@@ -2520,7 +2520,6 @@ def test_onchain_feechange(node_factory, bitcoind, executor):
     assert only_one(l2.rpc.listinvoices('onchain_timeout')['invoices'])['status'] == 'unpaid'
 
 
-@pytest.mark.skip("Lisa, please fix this!")
 @pytest.mark.developer("needs DEVELOPER=1 for dev-set-fees")
 def test_onchain_all_dust(node_factory, bitcoind, executor):
     """Onchain handling when we reduce output to all dust"""