RFR: 8277215: Remove redundancy in ReferenceProcessor constructor args

[Stefan Johansson]

On Wed, 17 Nov 2021 18:27:10 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> > it is a change in behavior
> 
> The value of `_discovery_is_mt` is different, but the external behavior is the same. `ReferenceProcessor::get_discovered_list` will have `id == 0` in both cases, returning the same discovered list.

Yes, and in `discover_reference(...)` we will use the non-mt path when adding to the list, but since we only have one thread this should be fine.

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PR: https://git.openjdk.java.net/jdk/pull/6412