Reduce auto_stub.py by removing python 2.6 support code.
Reduce auto_stub.py by removing python 2.6 support code.

This makes this file even easier to read and python 2.6 support is not needed
anymore.

R=iannucci@chromium.org
BUG=

Review URL: https://codereview.chromium.org/238233002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@265799 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools