vboot: deprecate and remove legacy UI code BUG=b:146399181, b:167643628 TEST=make clean && make runtests TEST=Build and flash to device BRANCH=none Cq-Depend: chromium:2512739 Signed-off-by: Joel Kitching <kitching@google.com> Change-Id: Ia8d95451d55142fbe9acaa6e49de9b5abe134083 Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2512740 Reviewed-by: Joel Kitching <kitching@chromium.org> Tested-by: Joel Kitching <kitching@chromium.org> Commit-Queue: Yu-Ping Wu <yupingso@chromium.org>