pnfs-obj: pnfs_osd_xdr: Remove dead code and cleanup

* Some leftovers from ancient times.
* This file will only define common types and client API.
  Remove server from comments

Signed-off-by: Boaz Harrosh &lt;Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>