RFR: 8342079: Shenandoah: Remove extra ShenandoahInitMarkRootsClosure

[William Kemper]

On Mon, 14 Oct 2024 18:42:53 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> `ShenandoahInitMarkRootsClosure` in `ShenandoahSTWMark` is semantically similar to the shared `ShenandoahMarkRefsClosure`. It misses subclassing the metadata-visiting superclass, though, and `ShenandoahMarkRefsClosure` does it right. It is cleaner and safer to use the super-class directly, as concurrent mark does it. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`

Marked as reviewed by wkemper (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/21504#pullrequestreview-2373331951