[ONNX] Fix flatten operator

[KsenijaS]

Even when dim is None, there are cases when flatten can be exported.
Also enable test_densenet in scripting mode

[codecov]

Codecov Report

Merging #45632 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master   #45632   +/-   ##
=======================================
  Coverage   68.63%   68.63%           
=======================================
  Files         406      406           
  Lines       52285    52285           
=======================================
  Hits        35885    35885           
  Misses      16400    16400           

Impacted Files	Coverage Δ
torch/onnx/symbolic_opset11.py	21.42% <0.00%> (ø)

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[neginraoof]

LGTM, Thanks!

[facebook-github-bot]

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

[facebook-github-bot]

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

[KsenijaS]

@bzinodev Can this PR be merged?

[dr-ci]

💊 CI failures summary and remediations

As of commit d4ba1f5 (more details on the Dr. CI page):

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• 2/2 failures possibly* introduced in this PR
  • 2/2 non-CircleCI failure(s)

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Extra GitHub checks: 1 failed

• Failed: Codecov - codecov/patch

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codecov.io: 1 failed

• Failed: codecov/patch

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[facebook-github-bot]

@bzinodev merged this pull request in 6ca03ae.