By making collection set regions (not candidates!) mark as not needing remembered set update, some checks in the calculations whether a reference should be enqueued can be simplified after JDK-8271880 as suggested by [~ayang].

Initial tests show this is correct because either
- the collection set region will be empty after gc and collected
- the collection set region will have failed evacuation but g1 currently never builds remembered sets for these regions

Do some more testing on this too.