revert misuse of programmatical approach in setup.py

[FCamborda]

setup.py was ditched a long time ago and newer PEPs recommend using setup.cfg or pyproject.toml

The last changes in setup.py created a misdirected dependency between requirements.txt and setup.py, which included an optional dependency that is causing problems upstreams.

This PR merely reverts those changes in favour for the old already-working setup.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1045f57) 34.49% compared to head (21993fd) 34.49%.

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Additional details and impacted files

@@ Coverage Diff @@## master #1303 +/- ##
=======================================
Coverage 34.49% 34.49% =======================================
Files 45 45 Lines 8257 8257 Branches 1146 1146 =======================================
Hits 2848 2848 Misses 5295 5295 Partials 114 114 

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