[heap] Remove ObjectMarking::BlackToWhite and ObjectMarking::GreyToWhite.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 8fec443c1bf5de1b1f8e1c09e1648bf6656a83f0..1439118719634c2a96c7a6b4eaa0c67c3804b8cc 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -78,20 +78,6 @@ class ObjectMarking : public AllStatic {
   }
 
   template <MarkingMode mode = MarkingMode::FULL>
-  V8_INLINE static void BlackToWhite(HeapObject* obj) {
-    DCHECK(IsBlack<mode>(obj));
-    MarkBit markbit = MarkBitFrom<mode>(obj);
-    Marking::BlackToWhite(markbit);
-    MemoryChunk::IncrementLiveBytes<mode>(obj, -obj->Size());
-  }
-
-  template <MarkingMode mode = MarkingMode::FULL>
-  V8_INLINE static void GreyToWhite(HeapObject* obj) {
-    DCHECK(IsGrey<mode>(obj));
-    Marking::GreyToWhite(MarkBitFrom<mode>(obj));
-  }
-
-  template <MarkingMode mode = MarkingMode::FULL>
   V8_INLINE static void BlackToGrey(HeapObject* obj) {
     DCHECK(IsBlack<mode>(obj));
     MarkBit markbit = MarkBitFrom<mode>(obj);