RFR: 8284572: Remove unneeded null check in ReferenceProcessor::discover_reference

[Kim Barrett]

On Fri, 8 Apr 2022 08:53:15 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of removing an always-false if-check.
> 
> Test: tier1-6

Looks good, now that we have JDK-8283415.

(Before JDK-8283415 someone could have potentially created a new
direct subclass of Reference, though doing so would probably run into
problems somewhere.)

I wonder if we could now completely eliminate REF_OTHER.  It looks
like the only class that can have that ref-type (after JDK-8283415) is
j.l.r.Reference.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8157