RFR: 8224814: Remove dead JNIHandleBlock freelist code

[Kim Barrett]

> On May 27, 2019, at 4:04 AM, Erik Österlund <erik.osterlund at oracle.com> wrote:
> 
> Hi,
> 
> The JNIHandleBlock used to be a shared structure between global and local JNI handles. The blocks have a freelist mechanism, that allows you to free individual handles inside of a block, by putting them on freelists. This freelist mechanism was used by global JNI handles. However, the global handles have moved into OopStorage, making the freelist mechanism effectively dead code. Let's remove it.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8224814
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8224814/webrev.00/
> 
> Thanks,
> /Erik

Thanks for cleaning this up.  I have a “note to self” to deal with this, but dropped the ball.
Hm, my notes suggest it might have been used for local jobjects via DestroyLocalRef,
and I hadn’t noticed that wasn’t true (any longer? or ever?).

Looks good.