Since change Ic5344ec34a130ee5a0ed2c7348af0b9d79e3508e which goes
back to Icehouse we've allowed using hw_watchdog_action for both
image metadata and flavor extra specs, even though you should
use hw:watchdog_action for flavor extra specs. Well, it's finally
time to remove the transition support for hw_watchdog_action in
flavor extra specs.
Change-Id: Ibf7bc549af498e2355ebdaf9e5d3337554a7f3d6