PM: Remove legacy PM (fix)

Source file was removed.  Need to remove docbook reference also.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Pavel Machek <pavel@suse.cz>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>