RFR: 8331660: Parallel: Cleanup includes in parallelScavangeHeap files

[Guoxiong Li]

On Fri, 3 May 2024 17:12:26 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> A trivial cleanup. Remove unused includes and moved includes close to use.

The additional `minimal-slowdebug` building succeeded locally. Looks good.

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Marked as reviewed by gli (Committer).

PR Review: https://git.openjdk.org/jdk/pull/19089#pullrequestreview-2039211720