channeldb: don't delete the chainHash bucket in CloseChannel
channeldb: don't delete the chainHash bucket in CloseChannel

In this commit, we fix an existing bug wherein if we closed two
channels, then we were unable to read the channel state afterwards as
we deleted the enclosing bucket.

aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd