Revert "thermal/core: Deprecate changing cooling device state from userspace"

This reverts commit a67a46af

.

It has been reported the warning is annoying as the cooling device
state is still needed on some production system.

Meanwhile we provide a way to consolidate the thermal framework to
prevent multiple actors acting on the cooling devices with conflicting
decisions, let's revert this warning.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>