RFR: 8357081: Removed unused methods of HexDigits

[Shaojin Wen]

In HexDigits, getCharsLatin1 and getCharsUTF16 are no longer used, so remove these methods

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Commit messages:
 - remove unused code

Changes: https://git.openjdk.org/jdk/pull/25258/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25258&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357081
  Stats: 69 lines in 1 file changed: 0 ins; 69 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25258.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25258/head:pull/25258

PR: https://git.openjdk.org/jdk/pull/25258