Get rid of duplicated CPU::DebugBreak() method.

src/cpu.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 41 matching lines @@
 
 class CPU : public AllStatic {
  public:
   // Initializes the cpu architecture support. Called once at VM startup.
   static void SetUp();
 
   static bool SupportsCrankshaft();
 
   // Flush instruction cache.
   static void FlushICache(void* start, size_t size);
-
-  // Try to activate a system level debugger.
-  static void DebugBreak();
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CPU_H_