RFR: 8340395: GenShen: Remove unnecessary check on card barrier flag

[Y. Srinivas Ramakrishna]

On Wed, 18 Sep 2024 16:41:04 GMT, William Kemper <wkemper at openjdk.org> wrote:

> PLABs will only be non-null in the generational mode, so we do not need to check the mode before checking if a PLAB is non-null.

Marked as reviewed by ysr (Committer).

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PR Review: https://git.openjdk.org/shenandoah/pull/501#pullrequestreview-2313765066