[lworld] RFR: 8329795: [lworld] Remove the jdk internal ValhallaFeatures test api

[Roger Riggs]

The api point jdk.internal.misc.ValhallaFeatures has been replaced by `--enable-preview` and `jdk.internal.misc.PreviewFeatures` and can be removed. 

The supporting files and test are removed.

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Commit messages:
 - 8329795: [lworld] Remove the jdk internal ValhallaFeatures test api

Changes: https://git.openjdk.org/valhalla/pull/1071/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1071&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329795
  Stats: 150 lines in 3 files changed: 0 ins; 150 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1071.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1071/head:pull/1071

PR: https://git.openjdk.org/valhalla/pull/1071