RFR: 8372977: unnecessary gthread-2.0 loading

[Phil Race]

On Wed, 3 Dec 2025 05:15:00 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

> Actual usage of the gthread-2.0 was removed with GTK2 support in [JDK-8329471](https://bugs.openjdk.org/browse/JDK-8329471).
> But there are some leftovers, we are still loading it with GTK3, even though it was never used when it was added in [JDK-8164321](https://bugs.openjdk.org/browse/JDK-8164321).
> 
> It wasn't an issue before, but some modern systems (e.g. openSUSE 16) don't provide the library.
> Because of this, we are unable to load GTK, which leads to Robot functionality requiring the Screencast or Remote Desktop API on Wayland not working.

Marked as reviewed by prr (Reviewer).

I see that testing looks good.

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PR Review: https://git.openjdk.org/jdk/pull/28625#pullrequestreview-3536103006
PR Comment: https://git.openjdk.org/jdk/pull/28625#issuecomment-3607898920