GitLab

Summary:
- Moving the unit test scripts from .circleci to .github
- Remove docker file for unit test base
- Use the Conda from Docker image in Linux jobs.

Remaining follow-up items

- Reuse the unittest script in Linux GPU job like done in Linux CPU job.

The unit test script needs to be fixed to be used for Linux GPU job
in new GHA workflow. Keeping it as a separate follow-up work item.

Pull Request resolved: https://github.com/pytorch/audio/pull/3407

Differential Revision: D46498263

Pulled By: mthrok

fbshipit-source-id: d8256717a55bb4257151d819d3b2ebd453601eac