git-cl: Fix some python3 compatibility errors.

Also, fix bug in git cl status where the 'updated' field was used to compare messages, even though
it doesn't exist (see [1]). This CL modifies it to use 'date', which does exist.

[1] https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#change-message-info

Bug: 1002209
Change-Id: I5a5e1193b8502c3ad35d94808ea178cad7f44ac6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1891259
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>