[lworld] Integrated: 8353752: [lworld] Remove handcoded offsets of field offsets for boxing classes

[Frederic Parain]

Remove hand coded offsets of boxing classes.

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Commit messages:
 - Remove hand code offets of boxing classes

Changes: https://git.openjdk.org/valhalla/pull/1421/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1421&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353752
  Stats: 68 lines in 2 files changed: 8 ins; 12 del; 48 mod
  Patch: https://git.openjdk.org/valhalla/pull/1421.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1421/head:pull/1421

PR: https://git.openjdk.org/valhalla/pull/1421