staging/lustre/osc: Get rid of osc_page_protected()

There was a proper debugging function by that name that's long
gone.
The currently remaining shadow that always returns true is not
really useful so it could be dropped along with all the
asserts it is part of.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>