GitLab

Summary:
Now that we do not build FFmpeg as part of CI build process, we can remove the pre/post build scripts.

Needs to land after https://github.com/pytorch/test-infra/pull/4358

Pull Request resolved: https://github.com/pytorch/audio/pull/3466

Reviewed By: atalman

Differential Revision: D47367022

Pulled By: mthrok

fbshipit-source-id: 17aafff74ee7d269236cffb8a88c803a8d4c44b7