make: remove checks for python 2 binary

This commit removes the checks for the Python 2 binary in the makefile
and makes sure that ZDTM tests always use python3. Since support for
Python 2 has been dropped, these checks are no longer needed.

Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

test/crit-recode.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 import pycriu
 import sys
 import os