RFR: 8338780: GenShen: Fix up some comments

[Kelvin Nilsen]

On Thu, 22 Aug 2024 17:20:49 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

> In https://github.com/openjdk/jdk/pull/20395 Aleksey provided some suggestions for improving various comments. This ticket gathers together several of those changes.
> 
> **Testing:**
> - [x] GHA
> - [x] SPECjbb w/GenShen
> - [x] jtreg:tier1
> - [ ] Codepipeline testing

src/hotspot/share/gc/shenandoah/heuristics/shenandoahGlobalHeuristics.cpp line 46:

> 44:   // we do the same here, but with the following adjustments for generational mode:
> 45:   //
> 46:   // In generational mode, the sort order within the data array is not strictly descending amounts

Given discussion below, this comment is not true for Global collections.  Since global collection do not preselect aged regions.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/484#discussion_r1727609774