RFR: 8336638: Parallel: Remove redundant mangle in PSScavenge::invoke

[Zhengyu Gu]

On Wed, 17 Jul 2024 10:02:22 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Trivial removing unnecessary clear at start of young-gc. Also move a precondition to the start, as early as possible.

LGTM and trivial

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Marked as reviewed by zgu (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20216#pullrequestreview-2182921091