chore(utxo-lib): remove unsafe non-segwit signing for zcash

Remove the unsafe non-segwit signing workaround from ZcashPsbt as it's
unnecessary. We now do this by default everywhere.

Issue: BTC-2286

Author: davidkaplanbitgo

modules/utxo-lib/src/bitgo/zcash/ZcashPsbt.ts

@@ -4,11 +4,10 @@ import {
   getDefaultVersionGroupIdForVersion,
   ZcashTransaction,
 } from './ZcashTransaction';
-import { Network, PsbtTransaction, Signer } from '../../';
+import { Network, PsbtTransaction } from '../../';
 import { Psbt as PsbtBase } from 'bip174';
 import * as types from 'bitcoinjs-lib/src/types';
-import { ValidateSigFunction } from 'bitcoinjs-lib/src/psbt';
-import { ProprietaryKeySubtype, PSBT_PROPRIETARY_IDENTIFIER, withUnsafeNonSegwit } from '../PsbtUtil';
+import { ProprietaryKeySubtype, PSBT_PROPRIETARY_IDENTIFIER } from '../PsbtUtil';
 const typeforce = require('typeforce');
 
 const CONSENSUS_BRANCH_ID_KEY = Buffer.concat([
@@ -124,17 +123,6 @@ export class ZcashPsbt extends UtxoPsbt<ZcashTransaction<bigint>> {
     this.tx.consensusBranchId = getDefaultConsensusBranchIdForVersion(network, version);
   }
 
-  // For Zcash transactions, we do not have to have non-witness UTXO data for non-segwit
-  // transactions because zcash hashes the value directly. Thus, it is unnecessary to have
-  // the previous transaction hash on the unspent.
-  signInput(inputIndex: number, keyPair: Signer, sighashTypes?: number[]): this {
-    return withUnsafeNonSegwit(this, super.signInput.bind(this, inputIndex, keyPair, sighashTypes));
-  }
-
-  validateSignaturesOfInput(inputIndex: number, validator: ValidateSigFunction, pubkey?: Buffer): boolean {
-    return withUnsafeNonSegwit(this, super.validateSignaturesOfInput.bind(this, inputIndex, validator, pubkey));
-  }
-
   private setPropertyCheckSignatures(propName: keyof ZcashTransaction<bigint>, value: unknown) {
     if (this.tx[propName] === value) {
       return;

modules/utxo-lib/test/bitgo/psbt/ZcashPsbt.ts

@@ -45,14 +45,11 @@ describe('Zcash PSBT', function () {
   describe('should be able to sign the transaction', function () {
     it('can sign the inputs', async function () {
       psbt.signAllInputsHD(rootWalletKeys.user);
-      assert(!(psbt as any).__CACHE.__UNSAFE_SIGN_NONSEGWIT);
       psbt.signAllInputsHD(rootWalletKeys.bitgo);
-      assert(!(psbt as any).__CACHE.__UNSAFE_SIGN_NONSEGWIT);
     });
 
     it('can validate the signatures on the unspents', async function () {
       psbt.validateSignaturesOfAllInputs();
-      assert(!(psbt as any).__CACHE.__UNSAFE_SIGN_NONSEGWIT);
     });
 
     it('can finalize and extract the transaction', async function () {