Delete useless assignments (#2939)

Author: CrazyHZM

dubbo-remoting/dubbo-remoting-api/src/main/java/org/apache/dubbo/remoting/transport/AbstractServer.java

@@ -45,7 +45,7 @@ public abstract class AbstractServer extends AbstractEndpoint implements Server
     private InetSocketAddress localAddress;
     private InetSocketAddress bindAddress;
     private int accepts;
-    private int idleTimeout = 600; //600 seconds
+    private int idleTimeout;
 
     public AbstractServer(URL url, ChannelHandler handler) throws RemotingException {
         super(url, handler);