RFR: 8337546: Remove unused GCCause::_adaptive_size_policy

Wed Jul 31 11:32:00 UTC 2024

Trivial removing an unused gc-cause; it was previously used by Parallel only.

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Commit messages:
 - remove-gc-cause

Changes: https://git.openjdk.org/jdk/pull/20403/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20403&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337546
  Stats: 13 lines in 4 files changed: 0 ins; 11 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20403.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20403/head:pull/20403

PR: https://git.openjdk.org/jdk/pull/20403