Revert "Generate files asyncronously"

Summary:
This reverts commit 5154859828d4f2ae027a23d0dd221c06eb5d41e1.
This was causing a cpu spin.

Test Plan: local build

Reviewers: jd, j, kt

Reviewed By: kt

Subscribers: eng

Differential Revision: http://phabricator.scale-data.com/D1036