[heap] Remove obsolete write barrier header inclusion.

R=mlippautz@chromium.org

Change-Id: I8ca8b899212786f78a0d42753aedbad02c211c06
Reviewed-on: https://chromium-review.googlesource.com/c/1426120Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59132}

src/heap/heap-inl.h

@@ -39,12 +39,6 @@
 #include "src/string-hasher.h"
 #include "src/zone/zone-list-inl.h"
 
-// The following header includes the write barrier essentials that can also be
-// used stand-alone without including heap-inl.h.
-// TODO(mlippautz): Remove once users of object-macros.h include this file on
-// their own.
-#include "src/heap/heap-write-barrier-inl.h"
-
 namespace v8 {
 namespace internal {