ctest: deprecate payload signing

Currently, ctest.py allows generating and testing signed payloads, but
that options has been disabled for long time and not being used. In
addition we are in the work of deprecating payload generation/signing
from devservers and this makes things much easier. Besides image signing
logic should not be here and I don't think it is necessary to test
signed payloads in VM as we can eaisly test them on real images. In
addition ctest is going to be deprecated sometimes soon and this helps
with that one too.

BUG=chromium:872441
TEST=betty-chrome-pfq-tryjob

Change-Id: Id5f92a49d82ac014f06098e38133dd8391046430
Reviewed-on: https://chromium-review.googlesource.com/1659436
Tested-by: Amin Hassani <ahassani@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
2 files changed