RFR: 8316021: Serial: Remove unused Generation::post_compact

Mon Sep 11 15:14:02 UTC 2023

Trivial removing dead code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/15663/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15663&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316021
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15663.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15663/head:pull/15663

PR: https://git.openjdk.org/jdk/pull/15663