Install torchao by default

[pytorchbot]

Summary:

Now that torchao is not experimental anymore, we can rely on torchao directly via git submodule.

Part of #7460

Test plan

CI

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/7712

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❌ 2 New Failures

As of commit 7b16b35 with merge base 9069017 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t b3147f77ecba425638ee903dc970b7df38c401dd7269cda2d9104c6f9a6a475e /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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