RFR [11]: Revert ClassLoaderDataGraphKlassIteratorStatic to upstream version

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/11-cleanup-cld/webrev.01/

Spotted this in our sh/jdk11 webrev. We have cleaned this up in sh/jdk:
  http://hg.openjdk.java.net/shenandoah/jdk/rev/26c2badedf17#l3.1

...but this never got into sh/jdk11.

Testing: tier3_gc_shenandoah, eyeballing webrev against upstream

Thanks,
-Aleksey