RFR: 8303083: (bf) Remove private DirectByteBuffer(long, int) constructor before JDK 21 GA

[Brian Burkhalter]

Remove the `DirectByteBuffer` constructor what was originally removed by #11873 and subsequently reinstated #12717.

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Commit messages:
 - 8303083: (bf) Remove private DirectByteBuffer(long, int) constructor before JDK 21 GA

Changes: https://git.openjdk.org/jdk/pull/12745/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12745&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303083
  Stats: 5 lines in 1 file changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12745.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12745/head:pull/12745

PR: https://git.openjdk.org/jdk/pull/12745