[heap] Delete wrong DCHECK.

This DCHECK is incorrect in no-snapshot builds because we can run 
garbage collection while deserializing the snapshot.

Bug: v8:6559, v8:6557
Change-Id: I0b8456ee19443f796889656952b236ff40b1e2fb
Reviewed-on: https://chromium-review.googlesource.com/600367Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Maya Lekova <mslekova@google.com>
Cr-Commit-Position: refs/heads/master@{#47130}

src/heap/heap.cc

@@ -6061,7 +6061,6 @@ void Heap::PrintAllocationsHash() {
 
 
 void Heap::NotifyDeserializationComplete() {
-  DCHECK_EQ(0, gc_count());
   PagedSpaces spaces(this);
   for (PagedSpace* s = spaces.next(); s != NULL; s = spaces.next()) {
     if (isolate()->snapshot_available()) s->ShrinkImmortalImmovablePages();