PCI: remove useless pci driver method

Remove pointless and never-called enable_wake() hook from pci_driver and
from documentation.  Evidently this was introduced in the 2.4.6 kernel,
but there's no evidence it was ever called; and it was rarely implemented.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>