Remove duplicate log under the case of session take over.

[DrmagicE]

When receiving a connection with a duplicate client id, gmqtt will print lots of duplicate logs in some situations, which is unnecessary and confusing.

2021-06-05T12:58:14.047+0800    INFO    server/server.go:497    logged in with new session      {"remote_addr": "127.0.0.1:58599", "client_id": "testing"}
2021-06-05T12:58:20.709+0800    INFO    server/server.go:323    logging with duplicate ClientID {"remote": "127.0.0.1:58600", "client_id": "testing"}
2021-06-05T12:58:20.709+0800    ERROR   server/client.go:247    connection lost {"client_id": "testing", "error": "operation error: Code = 8e, reasonString: "}
github.com/DrmagicE/gmqtt/server.(*client).setError.func1
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/client.go:247
sync.(*Once).doSlow
        /usr/local/go/src/sync/once.go:66
sync.(*Once).Do
        /usr/local/go/src/sync/once.go:57
github.com/DrmagicE/gmqtt/server.(*client).setError
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/client.go:245
github.com/DrmagicE/gmqtt/server.(*server).lockDuplicatedID
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/server.go:327
github.com/DrmagicE/gmqtt/server.(*server).registerClient
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/server.go:346
github.com/DrmagicE/gmqtt/server.(*client).connectWithTimeOut
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/client.go:674
github.com/DrmagicE/gmqtt/server.(*client).serve
        /usr/local/gopath/src/github.com/DrmagicE/gmqtt/server/client.go:1391
2021-06-05T12:58:20.709+0800    INFO    server/server.go:323    logging with duplicate ClientID {"remote": "127.0.0.1:58600", "client_id": "testing"}
2021-06-05T12:58:20.709+0800    INFO    server/server.go:323    logging with duplicate ClientID {"remote": "127.0.0.1:58600", "client_id": "testing"}
2021-06-05T12:58:20.709+0800    INFO    server/server.go:323    logging with duplicate ClientID {"remote": "127.0.0.1:58600", "client_id": "testing"}
2021-06-05T12:58:20.709+0800    INFO    server/server.go:323    logging with duplicate ClientID {"remote": "127.0.0.1:58600", "client_id": "testing"}