RFR: 8311821: Simplify ParallelGCThreadsConstraintFunc after CMS removal [v7]

[Thomas Schatzl]

On Wed, 26 Jul 2023 19:23:57 GMT, Jenny Shivayogi <duke at openjdk.org> wrote:

>> Code oddities reported by SonarCloud after CMS removal
>> Fix: moving ParallelGCThreadsConstraintFuncParallel to shared code as ParallelGCThreadsConstraintFunc
>
> Jenny Shivayogi has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fixing whitespace error

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/14965#pullrequestreview-1556912029