ACPI: Remove Kconfig symbol ACPI_PROCFS

Nothing cares about ACPI_PROCFS. This has been the case since v2.6.38.
This Kconfig symbol serves no purpose and its help text is now
misleading. It can safely be removed. If this symbol would be needed
again in the future it can be readded in a commit that adds code that
actually uses it.

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