fix: remove setup.cfg configuration for creating universal wheels (#13659)

The file `setup.cfg` contains a setting to create a Universal Wheel which is only needed if libraries support both Python 2 and Python 3. Python Cloud Client Libraries only support Python 3 so this setting is no longer needed. See https://packaging.python.org/en/latest/guides/distributing-packages-using-setuptools/#wheels. This will resolve the following warning in [this build log](https://github.com/googleapis/google-cloud-python/actions/runs/13822574147/job/38671145919?pr=13644) from PR #13644: ``` Building wheels for collected packages: googleapis-common-protos Building wheel for googleapis-common-protos (pyproject.toml): started Building wheel for googleapis-common-protos (pyproject.toml): finished with status 'error' error: subprocess-exited-with-error × Building wheel for googleapis-common-protos (pyproject.toml) did not run successfully. │ exit code: 1 ╰─> [40349 lines of output] running bdist_wheel /tmp/pip-build-env-9o_3w17v/overlay/lib/python3.13/site-packages/setuptools/_distutils/cmd.py:135: SetuptoolsDeprecationWarning: bdist_wheel.universal is deprecated !! ******************************************************************************** With Python 2.7 end-of-life, support for building universal wheels (i.e., wheels that support both Python 2 and Python 3) is being obviated. Please discontinue using this option, or if you still need it, file an issue with pypa/setuptools describing your use case. By 2025-Aug-30, you need to update your project and remove deprecated calls or your builds will no longer be supported. ******************************************************************************** !! ```

Author: parthea