libceph: kill ceph message bio_iter, bio_seg

The bio_iter and bio_seg fields in a message are no longer used, we
use the cursor instead.  So get rid of them and the functions that
operate on them them.

This is related to:
    http://tracker.ceph.com/issues/4428

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/include/linux/ceph/messenger.h b/include/linux/ceph/messenger.h
index 459e552..252e01b 100644
--- a/include/linux/ceph/messenger.h
+++ b/include/linux/ceph/messenger.h
@@ -121,11 +121,7 @@
 	enum ceph_msg_data_type		type;
 	union {
 #ifdef CONFIG_BLOCK
-		struct {
-			struct bio	*bio_iter;	/* iterator */
-			struct bio	*bio;
-			unsigned int	bio_seg;	/* current seg in bio */
-		};
+		struct bio		*bio;
 #endif /* CONFIG_BLOCK */
 		struct {
 			struct page	**pages;	/* NOT OWNER. */