RFR: 8303467: Serial: Refactor reference processor [v2]

[Albert Mingkun Yang]

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On Fri, 3 Mar 2023 16:05:38 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Simple refactoring and removing some unnecessary afterwards.
>> 
>> Test: tier1-5
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Thanks for the review.

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PR: https://git.openjdk.org/jdk/pull/12809