Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/payment/ConditionalEscrow.test.js

@@ -1,5 +1,5 @@
-import shouldBehaveLikeEscrow from './Escrow.behaviour';
-import EVMRevert from '../helpers/EVMRevert';
+const { shouldBehaveLikeEscrow } = require('./Escrow.behaviour');
+const { EVMRevert } = require('../helpers/EVMRevert');
 
 const BigNumber = web3.BigNumber;