GitHub Actions: do not install six in CI (#37361)

* GitHub Actions: do not install six in CI
* Remove workflow code that was commented out
* Remove any use of "six" from packages

.github/workflows/audit.yaml

@@ -25,7 +25,7 @@ jobs:
         python-version: ${{inputs.python_version}}
     - name: Install Python packages
       run: |
-        pip install --upgrade pip six setuptools pytest coverage[toml]
+        pip install --upgrade pip setuptools pytest coverage[toml]
     - name: Package audits (with coverage)
       if: ${{ inputs.with_coverage == 'true' }}
       run: |