RFR: 8337515: JVM_DumpAllStacks is dead code

[David Holmes]

Trivial cleanup of long unused code.

Thanks.

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Commit messages:
 - 8337515: JVM_DumpAllStacks is dead code

Changes: https://git.openjdk.org/jdk/pull/20396/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20396&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337515
  Stats: 11 lines in 2 files changed: 0 ins; 11 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20396.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20396/head:pull/20396

PR: https://git.openjdk.org/jdk/pull/20396