fix DubboCodec re-implements Codec2 #2977 (#3547)

Author: CrazyHZM

dubbo-rpc/dubbo-rpc-dubbo/src/main/java/org/apache/dubbo/rpc/protocol/dubbo/DubboCodec.java

@@ -27,7 +27,6 @@
 import org.apache.dubbo.common.utils.ReflectUtils;
 import org.apache.dubbo.common.utils.StringUtils;
 import org.apache.dubbo.remoting.Channel;
-import org.apache.dubbo.remoting.Codec2;
 import org.apache.dubbo.remoting.exchange.Request;
 import org.apache.dubbo.remoting.exchange.Response;
 import org.apache.dubbo.remoting.exchange.codec.ExchangeCodec;
@@ -45,7 +44,7 @@
 /**
  * Dubbo codec.
  */
-public class DubboCodec extends ExchangeCodec implements Codec2 {
+public class DubboCodec extends ExchangeCodec {
 
     public static final String NAME = "dubbo";
     public static final String DUBBO_VERSION = Version.getProtocolVersion();