[jdk17u-dev] RFR: 8297309: Memory leak in ShenandoahFullGC

[Aleksey Shipilev]

Clean backport to fix a trivial memory leak in Shenandoah.

Additional testing:
 - [x] Linux x86_64 fastdebug, `hotspot_gc_shenandoah`

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Commit messages:
 - Backport b80f5af6981440aec14f4dedbc5ee46364d0254c

Changes: https://git.openjdk.org/jdk17u-dev/pull/938/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=938&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297309
  Stats: 5 lines in 2 files changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/938.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/938/head:pull/938

PR: https://git.openjdk.org/jdk17u-dev/pull/938