RFR: 8331591: sun.font.CharSequenceCodePointIterator is buggy and unused

[Phil Race]

Delete an internal class that has been around for 20 years but never been used.
Verified that is true at least as far back as JDK7
All platforms build. Tests pass.

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Commit messages:
 - 8331591

Changes: https://git.openjdk.org/jdk/pull/19072/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19072&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331591
  Stats: 57 lines in 1 file changed: 2 ins; 55 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19072.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19072/head:pull/19072

PR: https://git.openjdk.org/jdk/pull/19072