Don't print owners comments when suggesting missing reviewers,
as this won't be supported when using Gerrit API.

Change-Id: I644b2f87b58a3c9ece3aa7d107100f3501bd3071
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2607675
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>