[pkg] Drop NO_SETUPTOOLS option
setuptools is the defacto standard nowadays. The only place where
NO_SETUPTOOLS option was used is during packaging (RPM, Debian) and even in
this context, it seems that setuptools is the way to go
(see https://wiki.debian.org/Python/LibraryStyleGuide).
../../doc/book usr/share/doc/cubicweb-documentation
../../doc/_build/html usr/share/doc/cubicweb-documentation