RFR: 8342679: Clean up PreviewFeature.Feature [v2]

[Aggelos Biboudis]

> After doing a build + bootcycle build confirms that these constants can be removed.

Aggelos Biboudis has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains two new commits since the last revision:

 - Update comment
 - 8342679: Clean up PreviewFeature.Feature

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21605/files
  - new: https://git.openjdk.org/jdk/pull/21605/files/8c948d22..0ff12dac

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21605&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21605&range=00-01

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21605.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21605/head:pull/21605

PR: https://git.openjdk.org/jdk/pull/21605