RFR: 8346569: Shenandoah: Worker initializes ShenandoahThreadLocalData twice results in memory leak

[William Kemper]

Clean backport, fixes memory leak.

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Commit messages:
 - Backport dfaa89162a35acd20b1ed35e147f9626a181510a

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/158/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=158&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346569
  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/158.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/158/head:pull/158

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/158