Issue #19936: Disable shebang lines in order to prevent using a random

system python.

Modules/_decimal/tests/bench.py

-#!/usr/bin/env python
-
 #
 # Copyright (C) 2001-2012 Python Software Foundation. All Rights Reserved.
 # Modified and extended by Stefan Krah.

Modules/_decimal/tests/deccheck.py

-#!/usr/bin/env python
-
 #
 # Copyright (c) 2008-2012 Stefan Krah. All rights reserved.
 #

Modules/_decimal/tests/randdec.py

-#!/usr/bin/env python
-
 #
 # Copyright (c) 2008-2012 Stefan Krah. All rights reserved.
 #