[debugger] remove some dead code.

src/debug/debug-frames.h

 // Copyright 2015 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_FRAMES_H_
 #define V8_DEBUG_DEBUG_FRAMES_H_
 
 #include "src/deoptimizer.h"
 #include "src/frames.h"
 #include "src/isolate.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 
 class FrameInspector {
  public:
   FrameInspector(JavaScriptFrame* frame, int inlined_jsframe_index,
                  Isolate* isolate);
 
   ~FrameInspector();
 
   int GetParametersCount();
-  int expression_count();
   Object* GetFunction();
   Object* GetParameter(int index);
   Object* GetExpression(int index);
   int GetSourcePosition();
   bool IsConstructor();
   Object* GetContext();
 
   JavaScriptFrame* GetArgumentsFrame() { return frame_; }
   void SetArgumentsFrame(JavaScriptFrame* frame);
 
@@ skipping 37 matching lines @@
 
   static StackFrame::Id UnwrapFrameId(int wrapped) {
     return static_cast<StackFrame::Id>(wrapped << 2);
   }
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_FRAMES_H_