[debugger] remove some dead code.

src/debug/debug.h

 // Copyright 2012 the V8 project 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 V8_DEBUG_DEBUG_H_
 #define V8_DEBUG_DEBUG_H_
 
 #include "src/allocation.h"
 #include "src/arguments.h"
 #include "src/assembler.h"
@@ skipping 420 matching lines @@
   void CreateDebugInfo(Handle<SharedFunctionInfo> shared);
   static Handle<DebugInfo> GetDebugInfo(Handle<SharedFunctionInfo> shared);
 
   template <typename C>
   bool CompileToRevealInnerFunctions(C* compilable);
 
   // This function is used in FunctionNameUsing* tests.
   Handle<Object> FindSharedFunctionInfoInScript(Handle<Script> script,
                                                 int position);
 
-  // Returns true if the current stub call is patched to call the debugger.
-  static bool IsDebugBreak(Address addr);
-
   static Handle<Object> GetSourceBreakLocations(
       Handle<SharedFunctionInfo> shared,
       BreakPositionAlignment position_aligment);
 
   // Check whether a global object is the debug global object.
   bool IsDebugGlobal(JSGlobalObject* global);
 
   // Check whether this frame is just about to return.
   bool IsBreakAtReturn(JavaScriptFrame* frame);
 
@@ skipping 302 matching lines @@
   static void PatchDebugBreakSlot(Isolate* isolate, Address pc,
                                   Handle<Code> code);
   static void ClearDebugBreakSlot(Isolate* isolate, Address pc);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_H_