RFR: 8365052: G1: Remove G1CollectionSet::groups() accessors

[Albert Mingkun Yang]

On Fri, 8 Aug 2025 08:11:10 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this small change that remove the public `G1CollectionSet::groups()` accessors because they are never used from outside the `G1CollectionSet` class.
> 
> Testing: local compilation, gha
> 
> Thanks,
>   Thomas

Marked as reviewed by ayang (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26688#pullrequestreview-3105757366