fix torchvision installation in tpu ci test setup script

[lsy323]

Currently in TPU CI, we are installing torch nightly whl before running tests, however, in TPU CI, torch_xla is built against PyTorch HEAD. This would cause some compatibility issues. (e.g. Symbol mismatching in .so)

• torchaudio is not needed for CI, remove torchaudio installation in the setup script as well.

• Instead of installing nightly torchvision, use the torchvision version pinned in PyTorch src folder.

[lsy323]

Cannot find a way to read the pytorch/.github/ci_commit_pins in test/tpu/xla_test_job.yaml.

When doing pip install "git+https://github.com/pytorch/vision.git@$TORCHVISION_COMMIT", $TORCHVISION_COMMIT will be an empty str.

To rule out the fact that we cannot change env var in the .yaml config files, I put the pip command in a shell script but looks like the path src/pytorch/.github/ci_commit_pins is not valid.

[lsy323]

Can you also mirror the fix to the GHA CI if it works? https://github.com/pytorch/xla/blob/master/.github/workflows/tpu_ci.yml

The commit pin will be more readily available.

I had a few attempts in the previous commits fixing the GHA TPU CI, but failed to do so, let's land the fix for installing torchvision properly for the old TPU CI.

[lsy323]

https://github.com/pytorch/xla/blob/master/.github/workflows/tpu_ci.yml

GHA TPU CI fixed in https://github.com/pytorch/xla/pull/6730