lib/model: Remove chatty delta index confirmation

This had its moment when making sure it worked initially, but nowadays
there is not point discussing the obvious on every folder on every
connect.

lib/model/model.go

@@ -808,7 +808,7 @@ func (m *Model) ClusterConfig(deviceID protocol.DeviceID, cm protocol.ClusterCon
 						continue
 					}
 
-					l.Infof("Device %v folder %q is delta index compatible (mlv=%d)", deviceID, folder.ID, dev.MaxSequence)
+					l.Debugf("Device %v folder %q is delta index compatible (mlv=%d)", deviceID, folder.ID, dev.MaxSequence)
 					startSequence = dev.MaxSequence
 				} else if dev.IndexID != 0 {
 					// They say they've seen an index ID from us, but it's