libceph: drop osdc from ceph_calc_raw_layout()

The osdc parameter to ceph_calc_raw_layout() is not used, so get rid
of it.  Consequently, the corresponding parameter in calc_layout()
becomes unused, so get rid of that as well.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>