backend: do not log error containing serialized tx

The error message coming from electrum contains the serialized
transaction and we do not want it in the logs, for privacy
reasons, so we strip it.

backend/coins/btc/electrum/client.go

@@ -18,6 +18,9 @@ import (
 	"bytes"
 	"context"
 	"encoding/hex"
+	"errors"
+	"fmt"
+	"strings"
 
 	"github.com/BitBoxSwiss/bitbox-wallet-app/backend/coins/btc/blockchain"
 	"github.com/BitBoxSwiss/bitbox-wallet-app/util/errp"
@@ -120,7 +123,8 @@ func (c *client) TransactionBroadcast(transaction *wire.MsgTx) error {
 	rawTxHex := hex.EncodeToString(rawTx.Bytes())
 	txID, err := c.client.TransactionBroadcast(context.Background(), rawTxHex)
 	if err != nil {
-		return err
+		// Return a new error, stripping the rawTxHex from it, if it is there.
+		return errors.New(strings.ReplaceAll(err.Error(), fmt.Sprintf("[%s]", rawTxHex), ""))
 	}
 	if txID != transaction.TxHash().String() {
 		return errp.New("Response is unexpected (transaction hash mismatch)")