RFR: 8364166: Parallel: Remove the use of soft_ref_policy in Full GC [v2]

[Albert Mingkun Yang]

> Simple removing redundant soft-ref-clearing checking in full-gc, because Parallel already reacts to this particular gc-cause, `_wb_full_gc`.
> 
> Test: tier1-3

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - review
 - Merge branch 'master' into pgc-soft-ref
 - pgc-soft-ref

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26496/files
  - new: https://git.openjdk.org/jdk/pull/26496/files/5d8f5956..ccef2df1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26496&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26496&range=00-01

  Stats: 1144 lines in 37 files changed: 604 ins; 386 del; 154 mod
  Patch: https://git.openjdk.org/jdk/pull/26496.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26496/head:pull/26496

PR: https://git.openjdk.org/jdk/pull/26496