RFR (S) 8243503: InstanceKlass::_array_name is not needed and leaks

[coleen.phillimore at oracle.com]

Summary: decrement the refcount for all Klass in class unloading.

See bug for more details.  Tested with tier1-6.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8243503.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8243503

Thanks,
Coleen