image_signing: drop support for signing nvidia lp0_firmware

This was only used by smaug which went EOL a while ago and we've
already deleted supporting logic.

BUG=None
TEST=CQ passes
BRANCH=None

Change-Id: Ia639c7da3c70c62ee102f11d510ffaa928ab244a
Signed-off-by: Mike Frysinger <vapier@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2309221
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
3 files changed