RFR: 8371205: AArch64: Remove unused cmpxchg* methods

[Hao Sun]

On Tue, 4 Nov 2025 13:41:04 GMT, Ruben <duke at openjdk.org> wrote:

> Since JDK-8364406, the AArch64 macroAssembler method cmpxchg_obj_header is no longer used. The method cmpxchgptr is used by cmpxchg_obj_header however is not used by any other method so can be removed alongside cmpxchgptr.
> cmpxchgw is also unused and can be removed.

Marked as reviewed by haosun (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/28131#pullrequestreview-3420572157