nfs: remove unused header <linux/pnfs_osd_xdr.h>

Commit 19fcae3 ("scsi: remove the SCSI OSD library") deleted the last
file that included <linux/pnfs_osd_xdr.h> but left that file behind.  It's
unused, get rid of it now.

Cc: Christoph Hellwig <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: [email protected]
Signed-off-by: Jonathan Corbet <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

Author: Jonathan Corbet