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.

chainntnfs/txnotifier.go

@@ -763,11 +763,9 @@ func (n *TxNotifier) CancelConf(confRequest ConfRequest, confID uint64) {
 	if confSet.details != nil {
 		confHeight := confSet.details.BlockHeight +
 			ntfn.NumConfirmations - 1
-		if confHeight <= n.currentHeight {
 		delete(n.ntfnsByConfirmHeight[confHeight], ntfn)
 	}
 }
-}
 
 // UpdateConfDetails attempts to update the confirmation details for an active
 // notification within the notifier. This should only be used in the case of a