fix pserver memory leak

paddle/fluid/operators/distributed/grpc/grpc_server.cc

@@ -107,9 +107,11 @@ class RequestSend final : public RequestBase {
     int trainer_id = request_->GetTrainerId();
     framework::Variable* outvar = nullptr;
 
+    /*
     if (!request_handler_->sync_mode()) {
       request_->ReleaseOwnershipOfLocalScope();
     }
+    */
     request_handler_->Handle(varname, scope, invar, &outvar, trainer_id);
     Finish(reply_, &responder_);
   }