The screen_stop function was removed some time ago together
with the screen support (I8c27182f60b0f5310b3a8bf5feb02beb7ffbb26a)
This does probably mean no proper horizon/grenade testing has been
done in the past 3 years...
Change-Id: I389e2a4f8135e0e22a70098b95c17457cbedf1cf