RFR: 8268537: (Temporary) Disable ParallelRefProcEnabled for Parallel GC

[Leo Korinth]

(Temporary) Disable ParallelRefProcEnabled for Parallel GC, will make Kitchensink pass.

Tier3 running, will wait for it before integrating.

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Commit messages:
 - 8268537:

Changes: https://git.openjdk.java.net/jdk/pull/4464/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4464&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268537
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4464.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4464/head:pull/4464

PR: https://git.openjdk.java.net/jdk/pull/4464