Fix 0x.js unused vars

packages/0x.js/test/artifacts_test.ts

@@ -1,4 +1,3 @@
-import * as chai from 'chai';
 import * as fs from 'fs';
 import HDWalletProvider = require('truffle-hdwallet-provider');
 
@@ -8,7 +7,6 @@ import {chaiSetup} from './utils/chai_setup';
 import {constants} from './utils/constants';
 
 chaiSetup.configure();
-const expect = chai.expect;
 
 // Those tests are slower cause they're talking to a remote node
 const TIMEOUT = 10000;