RFR: JDK-8269110: ZGC: Remove dead code in zBarrier

[Hamlin Li]

On Thu, 1 Jul 2021 11:54:30 GMT, Per Liden <pliden at openjdk.org> wrote:

>> this is a trivial cleanup to remove some dead code in zBarrier.
>
> Ok, so it looks like the bot reformated the commit message correctly anyway.

Thanks @pliden for review and comment, I'll use the correct PR title in the future.

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PR: https://git.openjdk.java.net/jdk/pull/4649