heap: Remove TraceTrait<T>::GetHeapObjectHeader

This method is not used and would not compile if we tried to use it.

Change-Id: I1d97d6ad4e0d3924e902a34e2ecc4d0a4c7604d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362893
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799197}

third_party/blink/renderer/platform/heap/trace_traits.h

@@ -164,11 +164,6 @@ struct TraceTrait {
     return {self, nullptr};
   }
 
-  static HeapObjectHeader* GetHeapObjectHeader(const void* self) {
-    return AdjustPointerTrait<T>::GetHeapObjectHeader(
-        static_cast<const T*>(self));
-  }
-
   static void Trace(Visitor*, const void* self);
 };