fix: remove setup.cfg configuration for creating universal wheels

[parthea]

setup.cfg contains a setting to create a Universal Wheel which is only needed if libraries support both Python 2 and Python 3. This library only supports Python 3 so this setting is no longer needed. See https://packaging.python.org/en/latest/guides/distributing-packages-using-setuptools/#wheels.

See similar PR googleapis/google-cloud-python#13659 which includes this stack trace

 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.
********************************************************************************
!!

[sycai]

Thanks!

[chalmerlowe]

Migration Notice: This library is moving to the google-cloud-python monorepo soon.

We closed this PR due to inactivity to ensure a clean migration. Please re-open this work in the new monorepo once the migration is complete!