[Doc] fix api reference

[ly015]

Motivation

Fix issues in API reference of MMPose docs

Modification

1. Remove redundant codes of transformer modules that cause unsuccessful doc compiling.
2. Add webcam API reference
3. Fix Windows CI

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (1.x@2489991). Click here to learn what that means.
Patch has no changes to coverable lines.

❗ Current head cbe7194 differs from pull request most recent head b02215c. Consider uploading reports for the commit b02215c to get more accurate results

Additional details and impacted files

@@          Coverage Diff           @@
##             1.x    #1792   +/-   ##
======================================
  Coverage       ?   79.51%           
======================================
  Files          ?      203           
  Lines          ?    11348           
  Branches       ?     1913           
======================================
  Hits           ?     9023           
  Misses         ?     1934           
  Partials       ?      391           

Flag	Coverage Δ
unittests	79.51% <0.00%> (?)

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