Remove __version__ in mmh3module.cpp

[hajimes]

I plan to remove the line

PyModule_AddStringConstant(module, "__version__", "3.1.0");

in mmh3module.cpp in the next non-trivial update.

The __version__ constant was introduced in 2.1 (2013-02-25), since it was in vogue back then and the only (iirc) way to get the version number of a module from within a python script.

However, Python 3.8 officially introduced importlib.metadata, which is no longer provisional in Python 3.10. Python 3.7 still needs to pip install importlib-metadata, but it will be in EOL soon. Therefore, there is no need to keep the __version__ constant anymore. Plus, keeping the same info in multiple files is a bad (very bad indeed) engineering practice.

See also
https://stackoverflow.com/a/72168209

I will bump up the version to 4.0.0 then, because the removal breaks backward compatibility, however minor it is.

[hajimes]

The removal of the constant has been done in version 4.0.0.