Revert "setup: use appropriate hooks to work around CFFI problems"

This reverts commit 241af49a8bf85f1c42625aebbd4f574ade862747. This
causes double compilation. There are more workarounds for this but I
don't want to to get a too big setup.py.
mib: don't encode CFFI version in generated module name

We don't want to recompile this module each time CFFI version
changes. Idea stolen from here:
 https://caremad.io/2014/11/distributing-a-cffi-project/