RFR: 8311656: Shenandoah: Unused ShenandoahSATBAndRemarkThreadsClosure::_claim_token

[Chad Rakoczy]

[JDK-8311656](https://bugs.openjdk.org/browse/JDK-8311656)

Remove unused `_claim_token` field from `ShenandoahSATBAndRemarkThreadsClosure`

Additional testing:
- [x] Linux x86_64 fastdebug `tier2`
- [x] Linux x86_64 release `tier2`
- [ ] Linux x86_64 fastdebug `test/hotspot/jtreg/gc/shenandoah`
- [ ] Linux x86_64 release `test/hotspot/jtreg/gc/shenandoah`
- [x] Linux x86_64 fastdebug `gtest:all`
- [x] Linux x86_64 release `gtest:all`

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

Commit messages:
 - 8311656: Shenandoah: Remove unused ShenandoahSATBAndRemarkThreadsClosure::_claim_token

Changes: https://git.openjdk.org/jdk/pull/14818/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14818&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311656
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14818.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14818/head:pull/14818

PR: https://git.openjdk.org/jdk/pull/14818