Integrated: 8326626: GenShen: Remove dead code associated with non-elastic TLABS

[Kelvin Nilsen]

Clean backport.

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Commit messages:
 - Backport 9fde64ecf7f4954dbd4028a57cdeb400de8b0268

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/25/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=25&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326626
  Stats: 8 lines in 1 file changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/25.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/25/head:pull/25

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/25