<i18n dev> RFR: 8311183: Remove unused mapping test files

[Naoto Sato]

There are unused charset mapping test files under `test/jdk/sun/nio/cs/mapping` directory, where one of them (`JIS0212.b2c.private`) has a questionable copyright header from the Unicode Consortium. They should be removed.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/14757/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14757&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311183
  Stats: 40027 lines in 6 files changed: 0 ins; 40027 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14757.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14757/head:pull/14757

PR: https://git.openjdk.org/jdk/pull/14757