first show: remove unnecessary code (#2968)

Co-authored-by: gabry <wu_shao_jie@qq.com>

dolphinscheduler-remote/src/main/java/org/apache/dolphinscheduler/remote/NettyRemotingServer.java

@@ -208,9 +208,7 @@ public class NettyRemotingServer {
                 if(workGroup != null){
                     this.workGroup.shutdownGracefully();
                 }
-                if(defaultExecutor != null){
                 defaultExecutor.shutdown();
-                }
             } catch (Exception ex) {
                 logger.error("netty server close exception", ex);
             }