Revert "[heap] Skip weak heap objects when sharedness doesn't match"

This reverts commit 38767476.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/43174/overview

Original change's description:
> [heap] Skip weak heap objects when sharedness doesn't match
>
> During marking, shared objects should not be marked when not
> marking the shared heap (i.e. when not doing a shared GC).
> Doing so is unsafe, as marking can race with sweeper threads
> sweeping the shared heap. This CL adds the missing check on
> weak object marking.
>
> Bug: v8:12687
> Change-Id: I1e0b8ba6b09bbcf665e5ff0f6242ed88f543c1fa
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3583610
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#79964}

Bug: v8:12687
Change-Id: If068d31f23a5280667dea1085b3076bb2107d07a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3584119
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Tobias Tebbi <tebbi@google.com>
Owners-Override: Tobias Tebbi <tebbi@google.com>
Cr-Commit-Position: refs/heads/main@{#79965}

src/heap/marking-visitor-inl.h

@@ -55,7 +55,6 @@ template <typename THeapObjectSlot>
 void MarkingVisitorBase<ConcreteVisitor, MarkingState>::ProcessWeakHeapObject(
     HeapObject host, THeapObjectSlot slot, HeapObject heap_object) {
   concrete_visitor()->SynchronizePageAccess(heap_object);
-  if (!is_shared_heap_ && heap_object.InSharedHeap()) return;
   if (concrete_visitor()->marking_state()->IsBlackOrGrey(heap_object)) {
     // Weak references with live values are directly processed here to
     // reduce the processing time of weak cells during the main GC