Remove broken codecov

[hugovk]

Codecov had deprecated their Python codecov package:

• https://about.codecov.io/blog/introducing-codecovs-new-uploader/

But rather than only deprecating it, they've completely deleted the package from PyPI:

• https://pypi.org/project/codecov/
• Codecov disappeared in PyPI? codecov/python-standard#31
• https://community.codecov.com/t/codecov-yanked-from-pypi-all-versions/4259?u=hugovk

This will cause CI failures.

Let's remove Codecov from Azure Pipelines. We're using the action for GitHub Actions.

[codecov]

Codecov Report

Merging #385 (7bfc006) into main (695a1a8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #385   +/-   ##
=======================================
  Coverage   99.61%   99.61%           
=======================================
  Files           8        8           
  Lines         770      770           
=======================================
  Hits          767      767           
  Misses          3        3           

Flag	Coverage Δ
macos-latest	99.61% <ø> (ø)
ubuntu-latest	99.61% <ø> (ø)
windows-latest	99.61% <ø> (ø)

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