chainntnfs/tx_notifier: remove cached conf details on reorg
chainntnfs/tx_notifier: remove cached conf details on reorg

In this commit, we address a small bug where it's possible to deliver a
confirmation notification with stale confirmation details upon
registration. This can happen if a transaction has confirmed but was
reorged out of the chain later on, and a subsequent notification is
registered.

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