Remove all BUILD_ and RUN_DEPENDS to allow this port to bootstrap other components needed to support PEP-517 packaging. Namely, this cannot depend on setuptools as latest setuptools (> 58) itself will eventually bootstrap from this and other components, especially after distutils is removed.
Still a WIP, not currently seeking approval to commit. check-stagedir.sh actually fails despite everything matching, confirmed via diff.
Successfully packages, passes QA and bootstraps its consumers.