[skip ci] complete k8s provider deleting pod logic (#4553)

Signed-off-by: yinghao.zou <yinghao.zou@zilliz.com>

shards/discovery/plugins/kubernetes_provider.py

@@ -170,7 +170,7 @@ class EventHandler(threading.Thread):
         self.terminate = True
 
     def on_drop(self, event, **kwargs):
-        pass
+        self.mgr.delete_pod(event['pod'])
 
     def on_pod_started(self, event, **kwargs):
         try_cnt = 3