[heap] Remove unused no marking scope.

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 1e75a177f8a40eb3b240bf23b59ee90c1a3a37e0..859ef603efa7669cdfb7a94af78b95fc59b57c8e 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -194,10 +194,6 @@ class IncrementalMarking {
 
   void NotifyOfHighPromotionRate();
 
-  void EnterNoMarkingScope() { no_marking_scope_depth_++; }
-
-  void LeaveNoMarkingScope() { no_marking_scope_depth_--; }
-
   void NotifyIncompleteScanOfObject(int unscanned_bytes) {
     unscanned_bytes_of_large_object_ = unscanned_bytes;
   }
@@ -291,8 +287,6 @@ class IncrementalMarking {
   intptr_t write_barriers_invoked_since_last_step_;
   size_t idle_marking_delay_counter_;
 
-  int no_marking_scope_depth_;
-
   int unscanned_bytes_of_large_object_;
 
   bool was_activated_;