Remove license classifiers

```
SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

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

License :: OSI Approved :: BSD License

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

Start by locating the template's Python packaging metadata and the license classifier named in the warning. Remove the deprecated classifier in favor of an SPDX license expression, then verify that the generated project no longer emits this warning.

Scritto dal modello di indicizzazione a partire dal testo della issue.