acpi: remove reference to ACPI_HOTPLUG_IO

The Kconfig entry for ACPI Container and Module Devices got
added in v2.6.11. Its default value has always been set to
    (ACPI_HOTPLUG_MEMORY || ACPI_HOTPLUG_CPU || ACPI_HOTPLUG_IO)

But the Kconfig symbol ACPI_HOTPLUG_IO has never existed. So it's
pointless to use it to set this default value.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>