RFR: 8224814: Remove dead JNIHandleBlock freelist code

[Erik Österlund]

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