RFR: 8286303: Serial: Remove reference to ParGCRareEvent_lock

[Thomas Schatzl]

Hi all,

  can I have reviews for this removal of an unused reference of ParGCRareEvent_lock in serial gc code - it is the only user of this BOT code, the other collectors have their own, completely separate one as far as I can tell.

Testing: gha, tier1-5

Thanks,
Thomas

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Depends on: https://git.openjdk.java.net/jdk/pull/8573

Commit messages:
 - Initial implementation

Changes: https://git.openjdk.java.net/jdk/pull/8576/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8576&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286303
  Stats: 5 lines in 2 files changed: 1 ins; 3 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8576.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8576/head:pull/8576

PR: https://git.openjdk.java.net/jdk/pull/8576