RFR: 8338336: GenShen: Cleanup stale TODOs [v2]

[William Kemper]

> Conflict with https://bugs.openjdk.org/browse/JDK-8332082, left barrier code in 21 unchanged.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Still have incremental mode in 21

-------------

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/82/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/82/files/bcefbbf1..6b41045b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=82&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=82&range=00-01

  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/82.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/82/head:pull/82

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/82