[lworld] RFR: 8376029: [lworld] Remove dead code related to preview mode

[David Beaumont]

Remove dead code and make functions private.

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Commit messages:
 - Remove dead code and make functions private

Changes: https://git.openjdk.org/valhalla/pull/1941/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1941&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376029
  Stats: 21 lines in 2 files changed: 2 ins; 11 del; 8 mod
  Patch: https://git.openjdk.org/valhalla/pull/1941.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1941/head:pull/1941

PR: https://git.openjdk.org/valhalla/pull/1941