[lworld] RFR: [lworld] code cleanup reverting some old leftover change

[Mandy Chung]

This patch reverts some leftover change from previous milestones which is unnecessary now.

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Commit messages:
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into inline-field
 - Revert unnecessary changes leftover in LW3
 - test fix
 - clean up
 - add new regression test
 - JDK-8260371: [lworld] Field::get should return default value instead of null on non-flattened inline field

Changes: https://git.openjdk.java.net/valhalla/pull/315/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=315&range=00
  Stats: 24 lines in 6 files changed: 9 ins; 14 del; 1 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/315.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/315/head:pull/315

PR: https://git.openjdk.java.net/valhalla/pull/315