Naming client may register the old one instance when reconnecting to server.

[KomachiSion]

Describe the bug
Current client naming will cache all registered service and instance so that It can redo the registering when reconnection.

But for nacos 2.0 server, one client connection only can register one instance for one service. So cache more instance for same instance is useless and using set to cache will make it disorder and register error instance when reconnection.

Expected behavior
Redo register the last registered instance for service.

Acutally behavior
Maybe register the old registered instance for service.

Desktop (please complete the following information):

• Version nacos-server 2.0.x, nacos-client 2.0.x
• Module naming
• SDK original

Additional context
If users keep registering the same service, the client might be OOM.