This removes the '-mode' flag from the emitted job descriptions.

TBR=nodir@chromium.org

Bug: 914196,914926
Change-Id: I94ab67f0969b198164fa3fc3ef64a649dcf941bd
Reviewed-on: https://chromium-review.googlesource.com/c/1376657Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>