* Use `prune **` to remove all files from the sdist
- c.f. https://packaging.python.org/guides/using-manifest-in/#manifest-in-commands
- "Setuptools also has undocumented support for ** matching zero or more characters including forward slash, backslash, and colon."
* Manually include all "default" files for a sdist in MANIFEST.in
- c.f. https://packaging.python.org/guides/using-manifest-in/#how-files-are-included-in-an-sdist
c.f. https://github.com/scikit-hep/pyhf/pull/1449