RFR: 8293090: Remove unused par_oop_since_save_marks_iterate_done

[Albert Mingkun Yang]

Trivial change of removing dead code.

Test: build

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/10078/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10078&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293090
  Stats: 6 lines in 1 file changed: 0 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10078.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10078/head:pull/10078

PR: https://git.openjdk.org/jdk/pull/10078