RFR: 8326722: Cleanup unnecessary forward declaration in collectedHeap.hpp

[Thomas Schatzl]

On Tue, 27 Feb 2024 02:19:14 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> Trivial cleanup

lgtm and trivial

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Marked as reviewed by tschatzl (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18018#pullrequestreview-1902847169