[debugger] remove some dead code.

src/debug/debug-frames.cc

Index: src/debug/debug-frames.cc
diff --git a/src/debug/debug-frames.cc b/src/debug/debug-frames.cc
index 29f7d3cac550fac248e688833199f8039a883ca3..012d29162234a6f26466b43bca5bdffc7926abb8 100644
--- a/src/debug/debug-frames.cc
+++ b/src/debug/debug-frames.cc
@@ -45,11 +45,6 @@ int FrameInspector::GetParametersCount() {
 }
 
 
-int FrameInspector::expression_count() {
-  return deoptimized_frame_->expression_count();
-}
-
-
 Object* FrameInspector::GetFunction() {
   return is_optimized_ ? deoptimized_frame_->GetFunction() : frame_->function();
 }