RFR: 8354542: Clean up x86 stubs after 32-bit x86 removal

[Andrew Dinn]

On Mon, 14 Apr 2025 18:58:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> This cleanup target various x86-specific stubs and related generators. 
> 
> Additional testing: 
>  - [x] Linux x86_64 server fastdebug, `all`

Looks good.

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Marked as reviewed by adinn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24633#pullrequestreview-2767628926