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Summary:
There is a single pre/post script needed for building torchaudio. This PR:
1. Removes the old conda-specific build script
2. Renames the wheel script to be a general name

Pull Request resolved: https://github.com/pytorch/audio/pull/2695

Reviewed By: kit1980

Differential Revision: D39631971

Pulled By: osalpekar

fbshipit-source-id: 52b49a6e792536b6264228c01ac356d247b18ea8