RFR: 8360220: Deprecate and obsolete ParallelRefProcBalancingEnabled

[Albert Mingkun Yang]

Deprecating `ParallelRefProcBalancingEnabled`, which is used only by Parallel and G1, and both have it enabled by default.

Disabling it offers little benefit, so removing it do reduce the number commandline flags.

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Commit messages:
 - deprecate-balance

Changes: https://git.openjdk.org/jdk/pull/25932/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25932&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8360220
  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25932.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25932/head:pull/25932

PR: https://git.openjdk.org/jdk/pull/25932