Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

truffle-config.js

@@ -1,6 +1,4 @@
 require('dotenv').config();
-require('babel-register');
-require('babel-polyfill');
 
 const HDWalletProvider = require('truffle-hdwallet-provider');