Reverts 15871bbf

This SR is kept separate because it is not part of SR tests.

This SR is kept separate because it is not part of current tests.

When using slapos.reboostrap to re-launch buildout with the version
of Python that was just installed, zc.buildout and its dependencies
are reinstalled for the new Python with the same egg versions. Thus
SRs which install Python 2 need to use Python-2-compatible versions
of setuptools, pip and wheel all along.

For this stack/slapos-py2.cfg is introduced.

Except for python2: keep beautifulsoup4=4.8.2.

beautifulsoup4=4.12.2 requires flit as build backend.

backcall=0.2.0 requires flit-core as build backend

entrypoints=0.3 rquires flit as build backend

pkgconfig=1.5.1 requires poetry as build backend.

Earlier version 1.22.0 does not support recent setuptools.

Latest version 1.26.2 has more complex build requirements,
left for later.

Now that buildout uses pip to correctly follow pyproject.toml,
cattrs=22.2.0 requires poetry as the build backend.

For now it's easier to install as wheel than to install poetry and
then use it as setup-egg for cattrs. This must be done eventually.

zc.buildout=2.7.1+slapos020 is SlapOS-patched buildout2 with support
for bootstrapping buildout3, required to be able to install buildout3.

Downgrade related eggs to pre-buildout3 versions as well.

Version up zc.buildout, pip and zc.recipe.egg.

Version up slapos.rebootstrap to adapt to buildout3.

Zope no longer serve XML-RPC in ERP5, unless it is explicitly enabled
using this.

See nexedi/erp5!1931

--enable-readline is broken:
  - it searches for readline.h instead of readline/readline.h
  - it does not abort when it fails to find headers
Use --with-readline-inc so that it sets HAVE_READLINE.

Also use the dedicated configure option to enable update limit.
And sqlite3 does not depend directly on ncurses.

See neoppod@71564067

See merge request !1566

See merge request !1576

See merge request nexedi/slapos!1572

to avoid the following error:
relocation R_X86_64_32S against `.rodata' can not be used when making a shared object; recompile with -fPIC

software/osie-coupler: keep the build source directory instead of having another open62541-source part.