orangefs: do not check possibly stale size on truncate

Let the server figure this out because our size might be out of date or
not present.

The bug was that

	xfs_io -f -t -c "pread -v 0 100" /mnt/foo
	echo "Test" > /mnt/foo
	xfs_io -f -t -c "pread -v 0 100" /mnt/foo

fails because the second truncate did not happen if nothing had
requested the size after the write in echo.  Thus i_size was zero (not
present) and the orangefs_setattr though i_size was zero and there was
nothing to do.

Signed-off-by: Martin Brandenburg <martin@omnibond.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Marshall <hubcap@omnibond.com>