RFR: 8341992: GenShen: Fix formatting, remove unreachable code, unused imports and unnecessary comments [v2]

[William Kemper]

> Improve hygiene for PR for JEP-404.

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

  Align one line function blocks

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/510/files
  - new: https://git.openjdk.org/shenandoah/pull/510/files/c21d514c..736d9c45

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=510&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=510&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/510.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/510/head:pull/510

PR: https://git.openjdk.org/shenandoah/pull/510