RFR: 8339870: Remove yet more stale TODOs

[William Kemper]

Clean

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Commit messages:
 - Backport b7405b19d531269ccb611cb5dc6a07f491a7b9de

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/102/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=102&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339870
  Stats: 318 lines in 15 files changed: 50 ins; 162 del; 106 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/102.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/102/head:pull/102

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/102