[lworld] Integrated: 8337115: [lworld] Whitebox API does not require --enable-preview

[David Simms]

Remove enable preview for WhiteBox, and some unnecessary @build InstructionHelper (its in the test lib already)

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Commit messages:
 - 8337115: [lworld] Whitebox API does not require --enable-preview

Changes: https://git.openjdk.org/valhalla/pull/1184/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1184&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337115
  Stats: 20 lines in 16 files changed: 0 ins; 20 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1184.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1184/head:pull/1184

PR: https://git.openjdk.org/valhalla/pull/1184