build(build-system): Remove setuptools build dependency

[tjni]

This was added in 3bc03fb to support pip install -e . but I noticed that (per python-poetry/poetry#34 (comment)), this is fixed in pip >= 21.3.

For context, I am working on this package in nixpkgs and investigating if setuptools is really needed as a build dependency.

[CLAassistant]

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[tjni]

I don't want to read and sign a CLA. Please feel free to do whatever you want with this minor code change.

[tony]

Thanks for helping on the package on nixpkgs.

I'd offer to have the CLA explained, but since you refused, yet also have this PR, I'm at an impasse.

[tony]

Released v0.22.2

[tjni]

Thank you for taking care of it.