Summary:
* Internally, we already set up babel before calling into metro-bundler.
* Externally, I moved the setup calls to outside the packager/ folder.
If somebody has a custom integration with RN, they would need to setup babel themselves up until we make the open source split. By the time this is released in open source, an npm version of metro-bundler will be available for use.
Next step: also do this for the worker and remove setupBabel from the metro repo.
Reviewed By: davidaurelio
Differential Revision: D5121429
fbshipit-source-id: e77c6ccc23bef1d13fd74c4727be2d7e09d2d0ca
17e0478cf4