message: chore(core): deprecate hdPath in transactionBuilder
  The `hdPath()` wrapper is not needed any longer.
  Issue:
diff: @@ -898,7 +898,6 @@ exports.signTransaction = function (params) {
  let rootExtKey;
  if (keychain) {
  rootExtKey = bitcoin.HDNode.fromBase58(keychain.xprv);
  - rootExtKeyPath = hdPath(rootExtKey);
  }
  const txb = bitcoin.TransactionBuilder.fromTransaction(transaction, network);
  @@ -920,13 +919,13 @@ exports.signTransaction = function (params) {
  }
  const chainPath = currentUnspent.chainPath;
  - if (rootExtKeyPath) {
  + if (rootExtKey) {
  let { walletSubPath = '/0/0' } = keychain;
  if (walletSubPath === 'm') {
  walletSubPath = ''
  }
  const path = keychain.path + walletSubPath + chainPath;
  - privKey = rootExtKeyPath.deriveKey(path);
  + privKey = rootExtKey.derivePath(path).keyPair;
  }
  privKey.network = network;
  