[VOL-1385] : Changes to support ONU delete
 Tested with,
1. ONU disable->delete
2. ONU delete
3. OLT delete

Change-Id: I8e6ff41a7ea8e94014700f274cb24fea73ac41f4
diff --git a/rw_core/mocks/device_manager.go b/rw_core/mocks/device_manager.go
index 116c7dc..6edfdc9 100644
--- a/rw_core/mocks/device_manager.go
+++ b/rw_core/mocks/device_manager.go
@@ -176,3 +176,8 @@
 func (dm *DeviceManager) ProcessTransition(previous *voltha.Device, current *voltha.Device) error {
 	return nil
 }
+
+// ChildDeviceLost -
+func (dm *DeviceManager) ChildDeviceLost(ctx context.Context, cDevice *voltha.Device) error {
+	return nil
+}