RFR: 8252089: psParallelCompact internal counters are global

[Albert Mingkun Yang]

Trivial change of removing debug-only counters.

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

Commit messages:
 - counter

Changes: https://git.openjdk.java.net/jdk/pull/3648/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3648&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252089
  Stats: 33 lines in 2 files changed: 0 ins; 33 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3648.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3648/head:pull/3648

PR: https://git.openjdk.java.net/jdk/pull/3648