RFR: 8329661: Refactor ScavengableNMethods::verify_unlisted_nmethods

[Albert Mingkun Yang]

Simple removing redundant verification.

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Commit messages:
 - s1-young-nmethod

Changes: https://git.openjdk.org/jdk/pull/18621/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18621&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329661
  Stats: 50 lines in 4 files changed: 0 ins; 45 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18621.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18621/head:pull/18621

PR: https://git.openjdk.org/jdk/pull/18621