Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/examples/SimpleToken.test.js

@@ -1,4 +1,4 @@
-import decodeLogs from '../helpers/decodeLogs';
+const { decodeLogs } = require('../helpers/decodeLogs');
 const SimpleToken = artifacts.require('SimpleToken');
 
 contract('SimpleToken', accounts => {