Revert "Arm backend: Add pypi package install option for VGF backend"

[metascroy]

Reverts #15551

This is causing internal test failures:

• Error outside of ExecuTorch: ModuleNotFoundError: No module named 'executorch.backends.arm.vgf.model_converter'

Errors inside of ExecuTorch:

• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:cos
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:custom_partition
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:debug_hook
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:decompose_avg_pool2d_pass
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:decompose_cosine_similarity_pass
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:decompose_div_pass
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:decompose_layernorm_pass
• buck test '@fbcode//mode/opt' fbcode//executorch/backends/arm/test:decompose_linalg_vector_norm_pass

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15681

• 📄 Preview Python docs built from this PR

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⏳ No Failures, 19 Pending

As of commit 5e5a724 with merge base 3dbc15b ():
💚 Looks good so far! There are no failures yet. 💚

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[github-actions]

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