Fix linter issues

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

@@ -33,13 +33,6 @@ const blockchainLifecycle = new BlockchainLifecycle(constants.RPC_URL);
 
 const NON_EXISTENT_ORDER_HASH = '0x79370342234e7acd6bbeac335bd3bb1d368383294b64b8160a00f4060e4d3777';
 
-function noError<T>(err: Error | null, value: T | undefined): value is T {
-    if (_.isNull(err)) {
-        throw err;
-    }
-    return _.isNull(err);
-}
-
 describe('ExchangeWrapper', () => {
     let web3: Web3;
     let zeroEx: ZeroEx;

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

@@ -1,6 +1,5 @@
 import { BlockchainLifecycle } from '@0xproject/dev-utils';
 import { BigNumber } from '@0xproject/utils';
-import * as chai from 'chai';
 import * as _ from 'lodash';
 import 'mocha';
 import * as Sinon from 'sinon';
@@ -15,7 +14,6 @@ import { assertNodeCallbackError } from './utils/report_callback_errors';
 import { web3Factory } from './utils/web3_factory';
 
 chaiSetup.configure();
-const expect = chai.expect;
 const blockchainLifecycle = new BlockchainLifecycle(constants.RPC_URL);
 
 describe('SubscriptionTest', () => {

packages/0x.js/test/utils/report_callback_errors.ts

@@ -1,7 +1,7 @@
 import * as chai from 'chai';
 import * as _ from 'lodash';
 
-import { DoneCallback, OrderState } from '../../src/types';
+import { DoneCallback } from '../../src/types';
 
 const expect = chai.expect;