vboot: Deprecate and remove EC-RO software sync

Remove the obsolete EC-RO software sync feature from the firmware. The
AP firmware no longer supports updating the EC RO region.

Deprecate the VB2_NV_TRY_RO_SYNC NVRAM parameter, treating it as a
no-op to preserve storage layout compatibility. Also remove the
try_ro_sync property from crossystem and clean up related tests.

BRANCH=none
BUG=b:518787337
TEST=Build and run tests

Change-Id: Ib38a8f272e142c644f324658976107035ecde794
Signed-off-by: Grzegorz Bernacki <bernacki@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/8084621
Reviewed-by: Julius Werner <jwerner@chromium.org>