RFR: 8282381: Parallel: Remove unnecessary PCReferenceProcessor

[Albert Mingkun Yang]

On Fri, 25 Feb 2022 07:14:21 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of removing a redundant class.
> 
> Test: tier1-5

I have compared 3 versions:

1. baseline (parent of 2 & 3)
2. this PR
3. oneline diff of using `nullptr` as the second arg of `PCReferenceProcessor` constructor.

and there's no significant diff among them running specjbb2015, specjvm2008, etc.

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PR: https://git.openjdk.java.net/jdk/pull/7618