ceph: Remove osd_client deadcode

osd_req_op_extent_osd_data_pagelist() was added in 2013 as part of
commit a4ce40a9 ("libceph: combine initializing and setting osd data")
but never used.

The last use of osd_req_op_cls_request_data_pagelist() was removed in
2017's commit ecd4a68a ("rbd: switch rbd_obj_method_sync() to
ceph_osdc_call()")

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>