RFR: 8358294: Remove unnecessary GenAlignment

[Thomas Schatzl]

On Mon, 2 Jun 2025 08:36:08 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple replacement of `GenAlignment` with `SpaceAlignment`, because they always have the same value. Removing the former to reduce complexity.
> 
> Test: tier1-3

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25577#pullrequestreview-2913607949