RFR: 8344151: GenShen: Improve comments, clean up unnecessary and unintended changes

[William Kemper]

Address a few style nits from: https://github.com/openjdk/jdk/pull/21273

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Commit messages:
 - Style and formatting fixes, revert unnecessary changes

Changes: https://git.openjdk.org/shenandoah/pull/536/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=536&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344151
  Stats: 10 lines in 4 files changed: 1 ins; 6 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah/pull/536.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/536/head:pull/536

PR: https://git.openjdk.org/shenandoah/pull/536