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>

include/acpi/acpi_bus.h

@@ -90,13 +90,11 @@ struct acpi_device;
 
 typedef int (*acpi_op_add) (struct acpi_device * device);
 typedef int (*acpi_op_remove) (struct acpi_device * device);
-typedef int (*acpi_op_start) (struct acpi_device * device);
 typedef void (*acpi_op_notify) (struct acpi_device * device, u32 event);
 
 struct acpi_device_ops {
 	acpi_op_add add;
 	acpi_op_remove remove;
-	acpi_op_start start;
 	acpi_op_notify notify;
 };