Python: Fix "implicit namespace packages" migration

... by omitting `__init__.py` from `crate` namespace package altogether,
see "PEP 420" [1] and "Package Discovery and Namespace Package » Finding
namespace packages" [2].

[1] https://peps.python.org/pep-0420/
[2] https://setuptools.pypa.io/en/latest/userguide/package_discovery.html#namespace-packages