Remove unused byte from Map::instance_sizes field.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index c1eda2a1de95e716cb9983c9497c26dff1f949c7..ace2eb65856afe7cad59d123c9355d411b6f6310 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1162,12 +1162,6 @@ class MacroAssembler: public Assembler {
                 Label* gc_required,
                 AllocationFlags flags);
 
-  // Undo allocation in new space. The object passed and objects allocated after
-  // it will no longer be allocated. Make sure that no pointers are left to the
-  // object(s) no longer allocated as they would be invalid when allocation is
-  // un-done.
-  void UndoAllocationInNewSpace(Register object);
-
   // Allocate a heap number in new space with undefined value. Returns
   // tagged pointer in result register, or jumps to gc_required if new
   // space is full.