[lworld] RFR: 8293868: [lworld] remove support for @__primitive__ and @__value__ for declaring primitive, value classes

[Vicente Romero]

This PR is removing support for, I think, experimental annotations `@__primitive__` and `@__value__`, there is no mention to them in any spec or JEP document

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Commit messages:
 - 8293868: [lworld] remove support for @__primitive__ and @__value__ for declaring primitive, value classes

Changes: https://git.openjdk.org/valhalla/pull/757/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=757&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293868
  Stats: 35 lines in 10 files changed: 0 ins; 17 del; 18 mod
  Patch: https://git.openjdk.org/valhalla/pull/757.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/757/head:pull/757

PR: https://git.openjdk.org/valhalla/pull/757