Stop logging payment preimages at INFO level

Payment preimages are proof-of-payment and correlation material. The INFO
log previously included the full preimage after a successful outbound
payment, exposing it to log collectors and anyone with log access.

Remove the preimage from the 'Successfully sent payment' log message in
src/event.rs, retaining only the payment hash for diagnostics. The
preimage remains accessible via the PaymentSuccessful event and payment
store APIs.

Author: elnafateh

src/event.rs

@@ -1225,16 +1225,14 @@ where
 					);
 					log_info!(
 						self.logger,
-						"Successfully sent payment of {}msat{} from \
-						payment hash {:?} with preimage {:?}",
+						"Successfully sent payment of {}msat{} with payment hash {}",
 						amount_msat,
 						if let Some(fee) = fee_paid_msat {
 							format!(" (fee {} msat)", fee)
 						} else {
 							"".to_string()
 						},
 						hex_utils::to_string(&payment_hash.0),
-						hex_utils::to_string(&payment_preimage.0)
 					);
 				});
 				let event = Event::PaymentSuccessful {