[heap] Remove dead code

Change-Id: I18190e902929d5b513b0a897faaddb8750f9b27a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3820066
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82316}

src/heap/heap.h

@@ -2220,10 +2220,6 @@ class Heap {
 
   LocalHeap* main_thread_local_heap_ = nullptr;
 
-  // List for tracking ArrayBufferExtensions
-  ArrayBufferExtension* old_array_buffer_extensions_ = nullptr;
-  ArrayBufferExtension* young_array_buffer_extensions_ = nullptr;
-
   // Determines whether code space is write-protected. This is essentially a
   // race-free copy of the {FLAG_write_protect_code_memory} flag.
   bool write_protect_code_memory_ = false;