cgpt: move to python3

This script is standalone, so move it over to Python 3 only.

BUG=chromium:981405
TEST=`./cgpt_unittest.py` passes

Change-Id: I47459ed672f563e7fa7de0215b36ce06386859ba
Reviewed-on: https://chromium-review.googlesource.com/1700159
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
2 files changed