RFR: 8357801: Parallel: Remove deprecated PSVirtualSpace methods

[Albert Mingkun Yang]

Simple removing some deprecated methods by changing to pointer-type for some fields.

Test: tier1-3

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Commit messages:
 - remove-more
 - pgc-remove-constructor

Changes: https://git.openjdk.org/jdk/pull/25459/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25459&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357801
  Stats: 42 lines in 6 files changed: 2 ins; 25 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/25459.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25459/head:pull/25459

PR: https://git.openjdk.org/jdk/pull/25459