rbd: kill ceph_osd_req_op->flags

The flags field of struct ceph_osd_req_op is never used, so just get
rid of it.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/osd_client.h

@@ -157,7 +157,6 @@ struct ceph_osd_client {
 
 struct ceph_osd_req_op {
 	u16 op;           /* CEPH_OSD_OP_* */
-	u32 flags;        /* CEPH_OSD_FLAG_* */
 	union {
 		struct {
 			u64 offset, length;