RFR: 8326975: Parallel: Remove redundant PSOldGen::is_allocated [v2]

[Albert Mingkun Yang]

> Simple removing redundant code, since old-gen should have been allocated in the caller context.
> 
> Test: tier1-3

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18047/files
  - new: https://git.openjdk.org/jdk/pull/18047/files/44340fbe..7f1ef376

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18047&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18047&range=00-01

  Stats: 4 lines in 3 files changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18047.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18047/head:pull/18047

PR: https://git.openjdk.org/jdk/pull/18047