thermal/of: Remove the thermal_zone_of_get_sensor_id() function

The function thermal_zone_of_get_sensor_id() is no longer used
anywhere, remove it.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20220818082316.2717095-2-daniel.lezcano@linaro.org