RFR: 8333486: Parallel: Remove unused methods in psParallelCompact

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - pgc-trivial

Changes: https://git.openjdk.org/jdk/pull/19539/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19539&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333486
  Stats: 18 lines in 2 files changed: 0 ins; 17 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19539.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19539/head:pull/19539

PR: https://git.openjdk.org/jdk/pull/19539