Python3: remove unused python2 code

BUG=chromium:1181635
TEST=None

Change-Id: I3b8e017340ac48f517e3b96cb6a5b7d40a096133
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2721064
Tested-by: Congbin Guo <guocb@chromium.org>
Auto-Submit: Congbin Guo <guocb@chromium.org>
Reviewed-by: Sanika Kulkarni <sanikak@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
Commit-Queue: Allen Li <ayatane@chromium.org>
3 files changed