txnotifier: delete ntfn by confirm height always
txnotifier: delete ntfn by confirm height always

When we cancel a confirmation request, we should remove the request from
the height map regardless of the current height. Otherwise we end up in
the situation when the height is reached, the notification is attempted
sent which results in a crash.

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