During the course of the code review and investigation surrounding JDK-8305334, visual examination of card-scanning code indicates that when old Reference objects on dirty cards are first discovered during a young collection they will continue to be on dirty cards.

There is code in reference processing in the `drop()` method (see PR code review for JDK-8305334 at https://github.com/openjdk/shenandoah/pull/238/files#r1153854386 ) that seems to do what appears to be an unnecessary card-mark.

This ticket is to investigate this closely and, if appropriate, elide the unnecessary check and card-mark.