Change CopyOnWriteArrayList to regular list in DubboProtocol (#4056)

Author: wavesZh

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

@@ -58,7 +58,6 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
-import java.util.concurrent.CopyOnWriteArrayList;
 
 import static org.apache.dubbo.common.constants.CommonConstants.GROUP_KEY;
 import static org.apache.dubbo.common.constants.CommonConstants.INTERFACE_KEY;
@@ -544,7 +543,7 @@ private void batchClientRefIncr(List<ReferenceCountExchangeClient> referenceCoun
      * @return
      */
     private List<ReferenceCountExchangeClient> buildReferenceCountExchangeClientList(URL url, int connectNum) {
-        List<ReferenceCountExchangeClient> clients = new CopyOnWriteArrayList<>();
+        List<ReferenceCountExchangeClient> clients = new ArrayList<>();
 
         for (int i = 0; i < connectNum; i++) {
             clients.add(buildReferenceCountExchangeClient(url));