mulit: remove ListLeasedOutputs in LeaseOutput

This commit removes the call toe `ListLeasedOutputs` in `LeaseOutput` -
the returned info from `ListLeasedOutputs` can easily be accessed via
`FetchInputInfo` and this info is only used at one callsite.
`ListLeasedOutputs` then becomes unnecessary here, plus it's very slow
and needs to be refactored in `btcwallet` instead.

lntest/mock/walletcontroller.go

@@ -195,9 +195,9 @@ func (w *WalletController) ListTransactionDetails(int32, int32,
 
 // LeaseOutput returns the current time and a nil error.
 func (w *WalletController) LeaseOutput(wtxmgr.LockID, wire.OutPoint,
-	time.Duration) (time.Time, []byte, btcutil.Amount, error) {
+	time.Duration) (time.Time, error) {
 
-	return time.Now(), nil, 0, nil
+	return time.Now(), nil
 }
 
 // ReleaseOutput currently does nothing.