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

[Thomas Schatzl]

On Fri, 1 Jul 2022 10:19:10 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of removing an unnecessary check. After that, the `enqueue` method becomes unused so removed as well.
> 
> Test: tier1-3

Lgtm. I closed [JDK-8258607](https://bugs.openjdk.org/browse/JDK-8258607) as duplicate of this as this change removes the last use of `SATBMarkQueue::enqueue`.

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Marked as reviewed by tschatzl (Reviewer).

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