Revert of Relax assert a little to fix flake on regress-3976

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index c4a368ea5b87cf564a5263c56dc05de002966d93..e89aafa900f5464348e4b934189fc00326fe5c09 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5656,7 +5656,7 @@
 class CheckHandleCountVisitor : public ObjectVisitor {
  public:
   CheckHandleCountVisitor() : handle_count_(0) {}
-  ~CheckHandleCountVisitor() { CHECK(handle_count_ < 2000); }
+  ~CheckHandleCountVisitor() { CHECK(handle_count_ < 1000); }
   void VisitPointers(Object** start, Object** end) {
     handle_count_ += end - start;
   }