usbcore: remove usb_suspend_root_hub

This patch (as740) removes the existing support for autosuspend of
root hubs.  That support fit in rather awkwardly with the rest of
usbcore and it was used only by ohci-hcd.  It won't be needed any more
since the hub driver will take care of autosuspending all hubs, root
or external.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>