thermal: trip: Drop redundant __thermal_zone_get_trip() header

The __thermal_zone_get_trip() header in drivers/thermal/thermal_core.h
is redundant, because there is one already in thermal.h, so drop it.

No functional impact.

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