RFR: 8342679: Clean up PreviewFeature.Feature [v3]

[Aggelos Biboudis]

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

Aggelos Biboudis has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java
  
  Co-authored-by: Chen Liang <liach at openjdk.org>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21605/files
  - new: https://git.openjdk.org/jdk/pull/21605/files/0ff12dac..8b778aff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21605&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21605&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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