RFR: 8289575: G1: Remove unnecessary is-marking-active check in G1BarrierSetRuntime::write_ref_field_pre_entry

Fri Jul 1 10:29:04 UTC 2022

Simple change of removing an unnecessary check. After that, the `enqueue` method becomes unused so removed as well.

Test: tier1-3

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Commit messages:
 - g1-pre-barrier-jrt-entry

Changes: https://git.openjdk.org/jdk/pull/9345/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9345&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289575
  Stats: 5 lines in 2 files changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9345.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9345/head:pull/9345

PR: https://git.openjdk.org/jdk/pull/9345