Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/tests/test_core.h

Index: ppapi/tests/test_core.h
===================================================================
--- ppapi/tests/test_core.h	(revision 109579)
+++ ppapi/tests/test_core.h	(working copy)
@@ -2,15 +2,13 @@
 // 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) {}
@@ -22,8 +20,6 @@
 
   std::string TestTime();
   std::string TestTimeTicks();
-
 };
 
-#endif  // PPAPI_TEST_TEST_CORE_H_
-
+#endif  // PPAPI_TESTS_TEST_CORE_H_