mds: do not send split_realms for CEPH_SNAP_OP_UPDATE msg

The clients won't care about the split_realms and the kclient will
treat this as a corrupted snaptrace.

Fixes commit 93e7267 ("mds: send snap
	related messages centrally during mds recovery")
Fixes: https://tracker.ceph.com/issues/61217
Signed-off-by: Xiubo Li <xiubli@redhat.com>
(cherry picked from commit 2131e1d)

Conflicts:
 - Misses a dependent commit 7a4c509

src/mds/MDCache.cc

@@ -6023,8 +6023,6 @@ void MDCache::finish_snaprealm_reconnect(client_t client, SnapRealm *realm, snap
 	     << realm->get_newest_seq() << " on " << *realm << dendl;
     auto snap = make_message<MClientSnap>(CEPH_SNAP_OP_UPDATE);
     snap->bl = realm->get_snap_trace();
-    for (const auto& child : realm->open_children)
-      snap->split_realms.push_back(child->inode->ino());
     updates.emplace(std::piecewise_construct, std::forward_as_tuple(client), std::forward_as_tuple(snap));
   } else {
     dout(10) << "finish_snaprealm_reconnect client." << client << " up to date"