remove LimitCores in c++ benchmark
diff --git a/test/cpp/qps/server.h b/test/cpp/qps/server.h
index c3d18e5..5f4c34c 100644
--- a/test/cpp/qps/server.h
+++ b/test/cpp/qps/server.h
@@ -51,7 +51,7 @@
 class Server {
  public:
   explicit Server(const ServerConfig& config) : timer_(new UsageTimer) {
-    cores_ = LimitCores(config.core_list().data(), config.core_list_size());
+    cores_ = gpr_cpu_num_cores();
     if (config.port()) {
       port_ = config.port();