RFR: 8332255: Shenandoah: Remove duplicate definition of init mark closure

[William Kemper]

8332255: Shenandoah: Remove duplicate definition of init mark closure

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Commit messages:
 - Remove duplicate definition of init mark closure

Changes: https://git.openjdk.org/jdk/pull/19238/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19238&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332255
  Stats: 23 lines in 1 file changed: 0 ins; 23 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19238.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19238/head:pull/19238

PR: https://git.openjdk.org/jdk/pull/19238