thermal: core: Drop unused .get_trip_*() callbacks

After recent changes in the ACPI thermal driver and in the Intel DTS
IOSF thermal driver, all thermal zone drivers are expected to use trip
tables for initialization and none of them should implement
.get_trip_type(), .get_trip_temp() or .get_trip_hyst() callbacks, so
drop these callbacks entirely from the core.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>