[lworld] RFR: 8373374: [lworld] Remove Unsafe.get/putValue

[Chen Liang]

Remove the old Unsafe getValue and putValue, which had some performance difficulties because they are megamorphic depending on the exact layout.

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Commit messages:
 - Remove get/putVal

Changes: https://git.openjdk.org/valhalla/pull/1782/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1782&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373374
  Stats: 265 lines in 9 files changed: 2 ins; 239 del; 24 mod
  Patch: https://git.openjdk.org/valhalla/pull/1782.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1782/head:pull/1782

PR: https://git.openjdk.org/valhalla/pull/1782