avocado/utils/kernel.py: remove executable support

Another instance of a non-executable file with a interpreter set.

This fixes the following errors spotted by rpmlint:

 E: wrong-script-interpreter
 /usr/lib/python2.7/site-packages/avocado/utils/kernel.py /usr/bin/env
 python
 E: non-executable-script
 /usr/lib/python2.7/site-packages/avocado/utils/kernel.py 644
 /usr/bin/env python
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/utils/kernel.py

-#!/usr/bin/env python
-
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation; either version 2 of the License, or