RFR: 8331683: Clean up GetCarrierThread

[Chris Plummer]

On Sat, 18 May 2024 00:47:59 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> JVMTI GetCarrierThread extension function was introduced by loom for testing.
> It's used by several tests in hotspot/jtreg/serviceability.
> 
> Testings: tier1..tier6

Marked as reviewed by cjplummer (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/19289#pullrequestreview-2069434194