RFR: 8378245: Obsolete ParallelRefProcBalancingEnabled

[Albert Mingkun Yang]

Obsolete `ParallelRefProcBalancingEnabled`, which has `true` as its default value.

Test: tier1

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

Commit messages:
 - obsolete-balance

Changes: https://git.openjdk.org/jdk/pull/29815/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29815&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378245
  Stats: 31 lines in 4 files changed: 1 ins; 29 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29815.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29815/head:pull/29815

PR: https://git.openjdk.org/jdk/pull/29815