[heap] Scavenger: Remove left-over

Also remove the comment on LayoutDescriptor as we want to pretenure
those.

Bug: chromium:738865
Change-Id: I5bdf66d383b481edc3250623e155b97d1081a7cc
Reviewed-on: https://chromium-review.googlesource.com/590235Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46970}

src/heap/scavenger-inl.h

@@ -238,9 +238,6 @@ void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object) {
   if (first_word.IsForwardingAddress()) {
     HeapObject* dest = first_word.ToForwardingAddress();
     DCHECK(object->GetIsolate()->heap()->InFromSpace(*p));
-    *p = dest;
-    // We require a relaxed store here since the slot might be in the map
-    // (e.g. LayoutDescriptor) and thus used for checking the layout.
     base::AsAtomicWord::Relaxed_Store(p, dest);
     return;
   }