RFR: 8345040: Clean up unused variables and code in `generate_native_wrapper`

[Hamlin Li]

On Tue, 26 Nov 2024 08:16:56 GMT, Qizheng Xing <qxing at openjdk.org> wrote:

> Some of variables and code are related to critical JNI natives feature, which was removed in JDK 18. This patch cleans them up.

Thanks for catching and fix.
riscv part looks good to me, seems other platforms have the similar issue, but good to have others have another look.

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Marked as reviewed by mli (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22384#pullrequestreview-2460890657