[ONNX] Add eliminate_unused_items pass

[KsenijaS]

This PR:

• Adds eliminate_unused_items pass that removes unused inputs and initializers.
• Fixes run_embed_params function so it doesn't export unnecessary parameters.
• Removes test_modifying_params in test_verify since it's no longer needed.

[KsenijaS]

@BowenBao @neginraoof please review

[dr-ci]

💊 CI failures summary and remediations

As of commit b72eb36 (more details on the Dr. CI page):

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💚 💚 Looks good so far! There are no failures yet. 💚 💚

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This comment has been revised 76 times.

[houseroad]

A high level question, won't general lint pass and dce pass work here?

[KsenijaS]

dce pass doesn't remove unused initializers and the only unused inputs that it removes are from prim:fork node: https://github.com/pytorch/pytorch/blob/master/torch/csrc/jit/passes/dead_code_elimination.cpp#L51

[BowenBao]

minor comment inline, LGTM

[KsenijaS]

@houseroad can you please review this.

[KsenijaS]

@houseroad flake8 and ci.pytorch.org test failure are not caused by this PR

[KsenijaS]

@houseroad clang-tidy failure is because of onnxTypeToScalarTypeMap in constant_fold pass:
https://github.com/pytorch/pytorch/blob/master/torch/csrc/jit/passes/onnx/constant_fold.cpp#L17

Do you have any other comment or can we merge this PR?

[houseroad]

Do you want to create some constant to address the issue?

[KsenijaS]

@houseroad I added constants ::ONNX_NAMESPACE::TensorProto_DataType_* to replace numbers 1 - 12 in onnxTypeToScalarTypeMap inside constant folding pass that were causing clang-tidy failure on the CI. However clang-tidy does not have the generated onnx header so it will still fail on the CI.
Do you want me to revert to previous state or keep the current code?

[KsenijaS]

@houseroad can we merge this PR?

[houseroad]

Can we let clang-tidy pass?

[BowenBao]

@houseroad please have a look, the clang-tidy issue is resolved. :)

[KsenijaS]

@houseroad CI is green, can we merge this PR?

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[facebook-github-bot]

@houseroad merged this pull request in 547ea78.