pm: remove obsolete piece of PM documentation

Remove some obsolete PM documentation.

The majority of contents of Documentation/power/pm.txt are
outdated.  Remove the outdated parts of this file and move the rest
to Documentation/power/apm-acpi.txt .  Update the index in
Documentation/power/ as appropriate.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/power/00-INDEX

@@ -1,5 +1,7 @@
 00-INDEX
 	- This file
+apm-acpi.txt
+	- basic info about the APM and ACPI support.
 basic-pm-debugging.txt
 	- Debugging suspend and resume
 devices.txt
@@ -14,8 +16,6 @@ notifiers.txt
 	- Registering suspend notifiers in device drivers
 pci.txt
 	- How the PCI Subsystem Does Power Management
-pm.txt
-	- info on Linux power management support.
 pm_qos_interface.txt
 	- info on Linux PM Quality of Service interface
 power_supply_class.txt