RFR: 8293622: Cleanup use of G1ConcRefinementThreads

[Lei Zaakjyu]

8293622: Cleanup use of G1ConcRefinementThreads

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Commit messages:
 - cleanup use of 'G1ConcRefinementThreads'

Changes: https://git.openjdk.org/jdk/pull/17080/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17080&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293622
  Stats: 6 lines in 3 files changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17080.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17080/head:pull/17080

PR: https://git.openjdk.org/jdk/pull/17080