Remove diamond key support from chromium.

This CL removes support for Diamond key. The feature was supported by
--has-chromeos-diamond-key Chromium flag.

Chrome OS side change: https://crrev.com/c/1474861

TEST=manual
BUG=929027

Change-Id: I0f338ca1776af59409068bd963c636fbc6ee3658
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1478571
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638453}
14 files changed