ACPI: thermal: Drop list of device ACPI handles from struct acpi_thermal

Notice that the list of device ACPI handles in struct acpi_thermal is not
used and drop it.

No functional impact.

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