thermal/core: Remove unused macro THERMAL_TRIPS_NONE

The macro THERMAL_TRIPS_NONE is no longer used, remove it.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Thara Gopinath <thara.gopinath@linaro.org>
Link: https://lore.kernel.org/r/20201214233811.485669-6-daniel.lezcano@linaro.org