Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/tests/test_core.h

 // Copyright (c) 2011 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 PPAPI_TEST_TEST_CORE_H_
-#define PPAPI_TEST_TEST_CORE_H_
+#ifndef PPAPI_TESTS_TEST_CORE_H_
+#define PPAPI_TESTS_TEST_CORE_H_
 
 #include <string>
 
 #include "ppapi/tests/test_case.h"
 
-struct PPB_Core;
-
 class TestCore : public TestCase {
  public:
   explicit TestCore(TestingInstance* instance) : TestCase(instance) {}
 
  private:
   // TestCase implementation.
   virtual bool Init();
   virtual void RunTest();
 
   std::string TestTime();
   std::string TestTimeTicks();
-
 };
 
-#endif  // PPAPI_TEST_TEST_CORE_H_
-
+#endif  // PPAPI_TESTS_TEST_CORE_H_