License classifiers are deprecated.

[jkroonza]

From Gentoo, the following QA warning:

 * QA Notice: setuptools warnings detected:
 * 
 * 	License classifiers are deprecated.

More info here:

https://peps.python.org/pep-0639/#deprecate-license-classifiers

And further explanation here:

pypa/setuptools#4938

[jkroonza]

/usr/lib/python3.13/site-packages/setuptools/dist.py:759: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: GNU General Public License (GPL)

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!

I note there's already a license= line, so looks like the one line above just needs to be removed.