RFR: 8342081: Shenandoah: Remove extra ShenandoahMarkUpdateRefsSuperClosure

[Y. Srinivas Ramakrishna]

On Mon, 14 Oct 2024 19:20:08 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> `ShenandoahMarkUpdateRefsSuperClosure` has only one real subclass, which is used in STW mark. We can collapse the class hierarchy a bit here. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`

lgtm

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Marked as reviewed by ysr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21505#pullrequestreview-2367773398