Fix Babel issues in tests by applying the right transforms

Created by: gaearon

This is a followup to #1177 with a less aggressive fix. For context, read threads #1156 (closed) and #1160 (closed).

Why this works:

• Babel has a bug where object/spread depends on parameters transform: https://github.com/babel/babel/issues/4851. So we have to enable parameters.
• Including regenerator transform in test environment was incorrect. Its async: false option only made sense for development and production configuration where we use babel-preset-latest, and so async functions are already being handled. But for test environment we use babel-preset-env instead of babel-preset-latest, and so including regenerator second time is redundant (and somehow breaks things—@hzoo could you clarify why this happened?)

I am remove destructuring and arrow-functions because they were added as stopgap measure in #1177 but turned out unnecessary per https://github.com/facebookincubator/create-react-app/issues/1156#issuecomment-265160544.

Fixes #1156 (closed) and #1160 (closed).