RFR: 8351700: Remove code conditional on BarrierSetNMethod being null [v2]

[Tom Rodriguez]

On Tue, 11 Mar 2025 20:00:59 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> All GCs started needing nmethod entry barriers as of loom so there's no longer any need to test for null nmethod entry barriers.
>
> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   revived accidentally deleted code

Marked as reviewed by never (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23996#pullrequestreview-2676195527