Remove `get_version_tuple()` Function

[michaelweinold]

Providing package version information through the use of a utility function is causing problems with empack:

• https://github.com/emscripten-forge/recipes/pull/616

It seems that with a more recent version of setuptools, this utility function would become obsolete:

As of the release of setuptools 61.0.0, one can specify the version dynamically in the project’s pyproject.toml file.

[michaelweinold]

...closing in favour of https://github.com/brightway-lca/bw_processing/pull/31