RFR: 8318801: Parallel: Remove unused verify_all_young_refs_precise

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - pgc-precise

Changes: https://git.openjdk.org/jdk/pull/16355/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16355&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318801
  Stats: 76 lines in 3 files changed: 0 ins; 76 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16355.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16355/head:pull/16355

PR: https://git.openjdk.org/jdk/pull/16355