Don't FC when a `channel_update` has a bogus `htlc_minimum_msat`

Don't FC when a `channel_update` has a bogus `htlc_minimum_msat`

If a peer sends us a `channel_update` for our own channel with an
`htlc_minimum_msat` which is more than the channel's amount, that's
dumb, but there's no reason to force-close the channel. We don't
even use the field.

Here we simply drop the unnecessary check.