RFR: 8283097: Parallel: Move filler object logic inside PSPromotionLAB::unallocate_object

[Albert Mingkun Yang]

On Mon, 14 Mar 2022 11:11:52 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple cleanup in the unallocation path in `PSPromotionManager::copy_unmarked_to_survivor_space`.
> 
> Test: hotspot_gc

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/7808