Convert win_helper.py to Python 3.
Convert win_helper.py to Python 3.

_winreg was renamed to winreg in Python 3.

Since we aren't maintaining Python 2 compatibility here, this removes
the future import to get print function behavior.

Change-Id: I4421cffa8280f80dc7556736ac57c8c353b7e576
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/mini_chromium/+/3547036
Reviewed-by: Justin Cohen <45f934f548b3ee92957d72fd2179b802430e9402@chromium.org>

chromium/mini_chromium,chromium/mini_chromium,chromium/mini_chromium