RFR: 8330002: Remove redundant public keyword in BarrierSet

[Albert Mingkun Yang]

Trivial removing redundant code.

-------------

Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/18708/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18708&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330002
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18708.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18708/head:pull/18708

PR: https://git.openjdk.org/jdk/pull/18708