RFR: 8331683: Clean up GetCarrierThread

[Alex Menkov]

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

Testings: tier1..tier6

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/19289/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19289&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331683
  Stats: 37 lines in 3 files changed: 4 ins; 27 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/19289.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19289/head:pull/19289

PR: https://git.openjdk.org/jdk/pull/19289