Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/token/ERC20/StandardToken.test.js

@@ -1,4 +1,4 @@
-import assertRevert from '../../helpers/assertRevert';
+const { assertRevert } = require('../../helpers/assertRevert');
 const StandardTokenMock = artifacts.require('StandardTokenMock');
 
 contract('StandardToken', function ([_, owner, recipient, anotherAccount]) {