[runtime] Remove dependency on the backing store age in DeleteCommon

Currently the function normalizes only old sparse backing stores.
This patch removed the age check to decouple the heuristic from GC.

Change-Id: I9b7f787315b2b8facfa35358143173f7d207c8da
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2846897Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74156}

src/objects/elements.cc

@@ -1904,12 +1904,10 @@ class FastElementsAccessor : public ElementsAccessorBase<Subclass, KindTraits> {
     backing_store->set_the_hole(isolate, entry);
 
     // TODO(verwaest): Move this out of elements.cc.
-    // If an old space backing store is larger than a certain size and
+    // If the backing store is larger than a certain size and
     // has too few used values, normalize it.
     const int kMinLengthForSparsenessCheck = 64;
     if (backing_store->length() < kMinLengthForSparsenessCheck) return;
-    // TODO(ulan): Check if it works with young large objects.
-    if (ObjectInYoungGeneration(*backing_store)) return;
     uint32_t length = 0;
     if (obj->IsJSArray()) {
       JSArray::cast(*obj).length().ToArrayLength(&length);

src/objects/js-objects-inl.h

@@ -775,7 +775,6 @@ static inline bool ShouldConvertToSlowElements(JSObject object,
   if (index - capacity >= JSObject::kMaxGap) return true;
   *new_capacity = JSObject::NewElementsCapacity(index + 1);
   DCHECK_LT(index, *new_capacity);
-  // TODO(ulan): Check if it works with young large objects.
   if (*new_capacity <= JSObject::kMaxUncheckedOldFastElementsLength ||
       (*new_capacity <= JSObject::kMaxUncheckedFastElementsLength &&
        ObjectInYoungGeneration(object))) {