Delete blimp/helium and remove references to it from dependent targets

blimp/helium/helium_test.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef BLIMP_HELIUM_HELIUM_TEST_H_
-#define BLIMP_HELIUM_HELIUM_TEST_H_
-
-#include "base/at_exit.h"
-#include "base/macros.h"
-#include "testing/gtest/include/gtest/gtest.h"
-
-namespace blimp {
-namespace helium {
-
-class HeliumTest : public ::testing::Test {
- public:
-  HeliumTest() {}
-  ~HeliumTest() override {}
-
- private:
-  base::ShadowingAtExitManager at_exit_manager_;
-
-  DISALLOW_COPY_AND_ASSIGN(HeliumTest);
-};
-
-}  // namespace helium
-}  // namespace blimp
-
-#endif  // BLIMP_HELIUM_HELIUM_TEST_H_