RFR: 8332864: Parallel: Merge ParMarkBitMapClosure into MoveAndUpdateClosure

[Albert Mingkun Yang]

Trivial merging a class into its subclass. (Some unused fields/args/methods are also removed.)

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Commit messages:
 - pgc-merge-class

Changes: https://git.openjdk.org/jdk/pull/19383/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19383&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332864
  Stats: 123 lines in 2 files changed: 28 ins; 79 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/19383.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19383/head:pull/19383

PR: https://git.openjdk.org/jdk/pull/19383