stop importing from easybuild.tools.py2vs3 (+ minor cleanup in init easyblocks test)

[boegel]

To fix deprecation warning being printed:

WARNING: Deprecated functionality, will no longer work in v6.0: Using py2vs3 is deprecated, since EasyBuild no longer runs on Python 2.; see http://easybuild.readthedocs.org/en/latest/Deprecated-functionality.html for more information

[boegel]

Test report by @boegel

Overview of tested easyconfigs (in order)

• SUCCESS Arriba-2.3.0-GCC-11.2.0.eb
• SUCCESS CD-HIT-4.8.1-GCC-11.3.0.eb

Build succeeded for 2 out of 2 (2 easyconfigs in total)
node3532.doduo.os - Linux RHEL 8.6, x86_64, AMD EPYC 7552 48-Core Processor (zen2), Python 3.6.8
See https://gist.github.com/boegel/3494e04af031bbb1d8d72b2cb11aa93d for a full test report.