Remove unnecessary wait for MPP tunnel destruction before shutdown

dbms/src/Server/FlashGrpcServerHolder.cpp

@@ -222,19 +222,6 @@ FlashGrpcServerHolder::~FlashGrpcServerHolder()
         LOG_INFO(log, "Begin to shut down flash grpc server");
         flash_grpc_server->Shutdown();
         *is_shutdown = true;
-        // Wait all existed MPPTunnels done to prevent crash.
-        // If all existed MPPTunnels are done, almost in all cases it means all existed MPPTasks and ExchangeReceivers are also done.
-        const int max_wait_cnt = 300;
-        int wait_cnt = 0;
-        while (GET_METRIC(tiflash_object_count, type_count_of_mpptunnel).Value() >= 1 && (wait_cnt++ < max_wait_cnt))
-            std::this_thread::sleep_for(std::chrono::seconds(1));
-        if (GET_METRIC(tiflash_object_count, type_count_of_mpptunnel).Value() >= 1)
-            LOG_WARNING(
-                log,
-                "Wait {} seconds for mpp tunnels shutdown, still some mpp tunnels are alive, potential resource leak",
-                wait_cnt);
-        else
-            LOG_INFO(log, "Wait {} seconds for mpp tunnels shutdown, all finished", wait_cnt);
 
         for (auto & cq : cqs)
             cq->Shutdown();