remove unused Debug::has_break_points_

Previous debug refactoring changes removed uses of has_break_points_, but
omitted removing the field itself. This is not necessary anymore.

R=yangguo@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1382443002

Cr-Commit-Position: refs/heads/master@{#31016}

src/debug/debug.h

@@ -592,7 +592,6 @@ class Debug {
   bool is_active_;
   bool is_suppressed_;
   bool live_edit_enabled_;
-  bool has_break_points_;
   bool break_disabled_;
   bool in_debug_event_listener_;
   bool break_on_exception_;