RFR: 8338280: Parallel: Inline ParallelCompactData::verify_clear

[Albert Mingkun Yang]

Trivial inlining a method to its sole caller.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/20561/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20561&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338280
  Stats: 9 lines in 2 files changed: 0 ins; 6 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20561.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20561/head:pull/20561

PR: https://git.openjdk.org/jdk/pull/20561