RFR: JDK-8267853: Remove unused styles from stylesheet

[Hannes Wallnöfer]

Please review a simple change to remove unused stylesheet classes, conveniently exposed by `CheckStylesheetClasses.java`. 

I have 1) grepped the generated documentation for the removed classes without finding any occurrences, and 2) compared the generated documentation in the browser page by page without finding any differences.

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Commit messages:
 - JDK-8267853: Remove unused styles from stylesheet

Changes: https://git.openjdk.java.net/jdk/pull/5601/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5601&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267853
  Stats: 49 lines in 3 files changed: 0 ins; 41 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5601.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5601/head:pull/5601

PR: https://git.openjdk.java.net/jdk/pull/5601