Bug#932820: vanguards: Use Python 3 instead of PyPy, because we are going to remove unsupported PyPy

[Ondrej Novy]

Hi,

yes, sorry for noise. After talk over IRC, current plan is:

* remove almost all pypy modules, keep only pypy interpreter (and maybe
setuptools, etc.)
* migrate to pypy3 (not possible now, waiting for tooling)

Thanks.

-- 
Best regards
 Ondřej Nový