Removed debug line from chai_setup. Its failing linter and does not appear to be used (it was from an old PR I merged in).

packages/metacoin/test/utils/chai_setup.ts

@@ -1,4 +1,3 @@
-import { BigNumber } from '@0xproject/utils';
 import * as chai from 'chai';
 import chaiAsPromised = require('chai-as-promised');
 import ChaiBigNumber = require('chai-bignumber');
@@ -10,12 +9,5 @@ export const chaiSetup = {
         chai.use(ChaiBigNumber());
         chai.use(dirtyChai);
         chai.use(chaiAsPromised);
-
-        // Node uses '.inspect()' instead of '.toString()' for log messages
-        // HACK: Typescript won't allow me to mess with BigNumber.prototype
-        // directly, so I create an instance and then get the prototype.
-        Object.getPrototypeOf(new BigNumber(0)).inspect = function() {
-            return this.toString();
-        };
     },
 };