RFR: Remove assertions constraining card marking for reference processing

[Kelvin Nilsen]

On Mon, 3 Apr 2023 20:58:25 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Shenandoah does _referent_ based processing for weak reference processing. We may see a mix of young and old references on the discovered list. We therefore need to mark cards for old references linked on the discovered list to young references to satisfy remembered set verification. These references may be mixed in any collection cycle.

(On the comment: we say failure to dirty the card may result in verification errors.  I think it may also result in failure to "take care" of interesting pointers, which can cause GC failures including crashes...  Or maybe this is strictly a verification problem, because the reference list is discarded before GC has to deal with these interesting pointers?)

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/241#pullrequestreview-1371412337