ACPI: Remove unused OSC_PCI_NATIVE_HOTPLUG

OSC_PCI_NATIVE_HOTPLUG is completely unused, so remove it.  No functional
change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>