[CI FIX]: remove the use of pkg_resources

[TenzDelek]

fixes #119

Problem

setuptools 82+ removed pkg_resourcespypa/setuptools#5174, which broke our CI. Our setup.py imported it to assert setuptools >= 38.6.0.

Solution:

Removed the assertion. It was a safeguard from 2017 when long_description_content_type was new.
Today, setuptools is in the 80+ range and pip itself requires a much newer version so The check would never fail in practice. current code was kind of deadcode

[TenzDelek]

CI Should work as expected. PTAL @eroux