[wrapper-tracing] Remove dead code leftover

Bug: chromium:841830
Change-Id: I0e00b0eca368d6471996288677eb45ea09a55977
Reviewed-on: https://chromium-review.googlesource.com/1071407Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561439}

third_party/blink/renderer/platform/bindings/script_wrappable_visitor.h

@@ -46,11 +46,6 @@ class TraceWrapperV8Reference;
 // wrapper references in traceable.
 class PLATFORM_EXPORT ScriptWrappableVisitor : public Visitor {
  public:
-  template <typename T>
-  static NOINLINE void MissedWriteBarrier() {
-    NOTREACHED();
-  }
-
   ScriptWrappableVisitor() : Visitor(ThreadState::Current()) {}
 
   // Trace all wrappers of |tracable|.