Removing listeners from deviceService at deactivation of Group and Flow managers to avoid NPE

Change-Id: Ia7526913e4f50b4c49ce9f2ae9ddf85c2db77a3a

@@ -160,6 +160,7 @@ public class FlowRuleManager
 
     @Deactivate
     public void deactivate() {
+        deviceService.removeListener(deviceListener);
         cfgService.unregisterProperties(getClass(), false);
         deviceInstallers.shutdownNow();
         operationsService.shutdownNow();

@@ -102,6 +102,7 @@ public class GroupManager
 
     @Deactivate
     public void deactivate() {
+        deviceService.removeListener(deviceListener);
         cfgService.unregisterProperties(getClass(), false);
         store.unsetDelegate(delegate);
         eventDispatcher.removeSink(GroupEvent.class);