[jdk17u-dev] RFR: 8320877: Shenandoah: Remove ShenandoahUnloadClassesFrequency support

[Aleksey Shipilev]

Clean backport to improve Shenandoah maintainability.

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

Commit messages:
 - Backport b65ccff357e2e294b027f693ceb3d25410236a6b

Changes: https://git.openjdk.org/jdk17u-dev/pull/2115/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2115&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320877
  Stats: 37 lines in 5 files changed: 0 ins; 34 del; 3 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2115.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2115/head:pull/2115

PR: https://git.openjdk.org/jdk17u-dev/pull/2115