RFR: 8330475: Remove unused default value for ModRefBarrierSet::write_ref_array_pre

[Albert Mingkun Yang]

Trivial removing unnecessary code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/18812/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18812&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330475
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18812.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18812/head:pull/18812

PR: https://git.openjdk.org/jdk/pull/18812