Revert "[heap] Verify client heaps during shared GC"

This reverts commit ddafb7a3.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20GC%20Stress%20-%20custom%20snapshot/43620/overview

Original change's description:
> [heap] Verify client heaps during shared GC
>
> With --verify-heap verify all client heaps before and after a shared
> GC. This ensures that the OLD_TO_SHARED remembered set is properly
> filled for each client isolate.
>
> Bug: v8:11708
> Change-Id: I1506a419c7a91c5baa87ce251da9861d8ad9e066
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3857559
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82829}

Bug: v8:11708
Change-Id: I421bce59211fe420b0893aaa9d35750ecaf23570
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3863282
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Owners-Override: Manos Koukoutos <manoskouk@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#82833}

src/heap/heap.cc

@@ -2434,30 +2434,12 @@ void Heap::PerformSharedGarbageCollection(Isolate* initiator,
     if (FLAG_concurrent_marking) {
       client->heap()->concurrent_marking()->Pause();
     }
-
-#ifdef VERIFY_HEAP
-    if (FLAG_verify_heap) {
-      // We don't really perform a GC here but need this scope for the nested
-      // SafepointScope inside Verify().
-      AllowGarbageCollection allow_gc;
-      HeapVerifier::VerifyHeap(client->heap());
-    }
-#endif  // VERIFY_HEAP
   });
 
   const GarbageCollector collector = GarbageCollector::MARK_COMPACTOR;
   PerformGarbageCollection(collector, gc_reason, nullptr);
 
   isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
-#ifdef VERIFY_HEAP
-    if (FLAG_verify_heap) {
-      // We don't really perform a GC here but need this scope for the nested
-      // SafepointScope inside Verify().
-      AllowGarbageCollection allow_gc;
-      HeapVerifier::VerifyHeap(client->heap());
-    }
-#endif  // VERIFY_HEAP
-
     if (FLAG_concurrent_marking &&
         client->heap()->incremental_marking()->IsMarking()) {
       client->heap()->concurrent_marking()->RescheduleJobIfNeeded();