ACPI: Drop device start operation that is not used

The ACPI device start operation, acpi_op_start, is never used, so
drop it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Merge branch 'acpi-cleanup-next' into bleeding-edge

* acpi-cleanup-next:
  ACPI: Drop device start operation that is not used
  ACPI: Remove useless type argument of driver .remove() operation