iwlwifi: mvm: Drop unused fw_trips_index[] from iwl_mvm_thermal_device

The fw_trips_index[] array in struct iwl_mvm_thermal_device is only
populated, but never read, so drop it.

Note that the iwl_mvm_send_temp_report_ths_cmd() code populating
fw_trips_index[] is questionable, because it accesses a trips table
of a thermal zone directly, which is not guaranteed to work in the
future.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Miri Korenblit <Miriam.rachel.korenblit@intel.com>