Make BUILDOUT-NEXT test suite use same setuptools version as master again
In 51740961 we "started testing new version of setuptools" and BUILDOUT-NEXT test suite was set to use this software/buildout-testing/software-next.cfg.
In https://lab.nexedi.com/nexedi/slapos/merge_requests/425 we started to depend on very recent setuptools and updated to 40.4.3 .
This software/buildout-testing/software-next.cfg kept using this old setuptools and BUILDOUT-NEXT test suite failed to build in a loop.
The test suite was already changed to use software/buildout-testing/software.cfg (ie. it's same as BUILDOUT but testing slapos.buildout's next branch instead of master ), so I think this profile is not needed currently.