autotest[py3] - removing py2 hashbangs

tests don't need them, nor should use them. The tools all have been
migrated so lets just flip the bit.

BUG=b:187788514
TEST=cq,unittests

Change-Id: Ib1326ff3ea19f0b13a4783c85261fc27691df262
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/3367231
Tested-by: Derek Beckett <[email protected]>
Reviewed-by: Jesse McGuire <[email protected]>
Commit-Queue: Derek Beckett <[email protected]>
diff --git a/client/tools/make_clean b/client/tools/make_clean
index 4283977..9cee4f5 100755
--- a/client/tools/make_clean
+++ b/client/tools/make_clean
@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/python3
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function