Clean up CI scripts

[mthrok]

• 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.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/audio/3407

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 2 New Failures

As of commit 3017b6a:

NEW FAILURES - The following jobs have failed:

• build (3.8) (gh)
• unittests-windows-gpu / windows-job (gh)

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[facebook-github-bot]

@mthrok has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@mthrok has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@mthrok merged this pull request in f080315.

[github-actions]

Hey @mthrok.
You merged this PR, but labels were not properly added. Please add a primary and secondary label (See https://github.com/pytorch/audio/blob/main/.github/process_commit.py).

---

Some guidance:

Use 'module: ops' for operations under 'torchaudio/{transforms, functional}', and ML-related components under 'torchaudio/csrc' (e.g. RNN-T loss).

Things in "examples" directory:

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• 'tutorial' is applicable to tutorials under the “examples/tutorials” folder
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Regarding examples in code documentations, please also use 'module: docs'.

Please use 'other' tag only when you’re sure the changes are not much relevant to users, or when all other tags are not applicable. Try not to use it often, in order to minimize efforts required when we prepare release notes.

---

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Things related to build are by default excluded from the release note, except when it impacts users. For example:
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