RFR: 8301555: Remove constantPoolCacheKlass friend

[Coleen Phillimore]

Please review this trivial change.

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Commit messages:
 - 8301555: Remove constantPoolCacheKlass friend

Changes: https://git.openjdk.org/jdk/pull/12349/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12349&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301555
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12349.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12349/head:pull/12349

PR: https://git.openjdk.org/jdk/pull/12349