RFR: (sh/jdk11): Move has_object_fields() from shared to shenandoah

[Roland Westrelin]

> http://cr.openjdk.java.net/~rkennke/shjdk11-hasobjfields/webrev.01/

jdk/jdk has a simpler implementation for has_object_fields():

bool ciInstanceKlass::has_object_fields() const {
  GUARDED_VM_ENTRY(
      return get_instanceKlass()->nonstatic_oop_map_size() > 0;
    );
}

Can we use that instead?

Roland.