Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/helpers/EVMThrow.js

@@ -1 +1,5 @@
-export default 'invalid opcode';
+const EVMThrow = 'invalid opcode';
+
+module.exports = {
+  EVMThrow,
+};