build: only support python3 binary

python2 will be end of life by the time of the next
libvirt release. All our supported build targets, including
CentOS7, have a python3 build available.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

scripts/mock-noinline.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2017-2019 Red Hat, Inc.
 #
@@ -16,8 +16,6 @@
 # License along with this library.  If not, see
 # <http://www.gnu.org/licenses/>.
 
-from __future__ import print_function
-
 import re
 import sys