swap: remove redundant prepayment probe

The prepayment probe, which includes the expected payment amount
for the fee invoice, is conducted at the start of the swapout.
The prepayment probe at this stage is inaccurate
and may cause unnecessary communication, so it will be removed.

swap/service.go

@@ -391,14 +391,6 @@ func (s *SwapService) SwapOut(peer string, chain string, channelId string, initi
 		return nil, fmt.Errorf("exceeding spendable amount_msat: %d", sp)
 	}
 
-	success, failureReason, err := s.swapServices.lightning.ProbePayment(channelId, amtSat*1000)
-	if err != nil {
-		return nil, err
-	}
-	if !success {
-		return nil, fmt.Errorf("the prepayment probe was unsuccessful: %s", failureReason)
-	}
-
 	swap := newSwapOutSenderFSM(s.swapServices, initiator, peer)
 	err = s.lockSwap(swap.SwapId.String(), channelId, swap)
 	if err != nil {