Delete flaky benchmark test

tests/benchmark/benchmark_nbody.cc

-// Copyright 2014 The Native Client Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
-#include <string>
-
-// @EXEMPTION[include]
-#include "./framework.h"
-
-
-extern "C" {
-  int main_nbody(int argc, const char* argv[]);
-}
-
-namespace {
-
-// Wrap NBody in benchmark harness
-class BenchmarkNBody : public Benchmark {
- public:
-  virtual int Run() {
-    const char *args[] = {"nbody", "500000"};
-    return main_nbody(2, args);
-  }
-  virtual const std::string Name() { return "NBody"; }
-  virtual const std::string Notes() { return "c #1 version"; }
-};
-
-}  // namespace
-
-// Register an instance to the list of benchmarks to be run.
-RegisterBenchmark<BenchmarkNBody> benchmark_nbody;