Avoid refusing ChannelMonitorUpdates we expect to receive after closing

Avoid refusing ChannelMonitorUpdates we expect to receive after closing

There is no need to fill the user's logs with errors that are expected
to be hit based on specific edge cases, like providing preimages after
a monitor has seen a confirmed commitment on-chain.

This doesn't really change our behavior – we still apply and persist the
state changes resulting from processing these updates regardless of
whether they succeed or not.