RFR: 8301459: Serial: Merge KeepAliveClosure into FastKeepAliveClosure

Tue Jan 31 08:55:38 UTC 2023

Simple removing unnecessary type hierarchy.

Test: hotspot_gc

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Commit messages:
 - s1-keep-alive

Changes: https://git.openjdk.org/jdk/pull/12310/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12310&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301459
  Stats: 53 lines in 3 files changed: 1 ins; 50 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12310.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12310/head:pull/12310

PR: https://git.openjdk.org/jdk/pull/12310