Free holding cell on monitor-updating-restored when there's no upd

Free holding cell on monitor-updating-restored when there's no upd

If there is no pending channel update messages when monitor updating
is restored (though there may be an RAA to send), and we're
connected to our peer and not awaiting a remote RAA, we need to
free anything in our holding cell.

Without this, chanmon_fail_consistency was able to find a stuck
condition where we sit on an HTLC failure in our holding cell and
don't ever handle it (at least until we have other actions to take
which empty the holding cell).

Still, this approach sucks - it introduces reentrancy in a
particularly dangerous form:
 a) we re-enter user code around monitor updates while being called
    from user code around monitor updates, making deadlocks very
    likely (in fact, our current tests have a bug here!),
 b) the re-entrancy only occurs in a very rare case, making it
    likely users will not hit it in testing, only deadlocking in
    production.
I'm not entirely sure what the alternative is, however - we could
move to a world where we poll for holding cell events that can be
freed on our 1-minute-timer, but we still have a super rare
reentrancy case, just in timer_chan_freshness_every_min() instead.