Simplify and properly implement openloop testing.
Revive it in tests as well
diff --git a/test/cpp/qps/client_sync.cc b/test/cpp/qps/client_sync.cc
index d93537b..edfc246 100644
--- a/test/cpp/qps/client_sync.cc
+++ b/test/cpp/qps/client_sync.cc
@@ -84,11 +84,8 @@
 
  protected:
   void WaitToIssue(int thread_idx) {
-    grpc_time next_time;
-    if (NextIssueTime(thread_idx, &next_time)) {
-      gpr_timespec next_timespec;
-      TimepointHR2Timespec(next_time, &next_timespec);
-      gpr_sleep_until(next_timespec);
+    if (!closed_loop_) {
+      gpr_sleep_until(NextIssueTime(thread_idx));
     }
   }