RFR (XS) 8210559: ClassLoaderData Symbols can leak

[coleen.phillimore at oracle.com]

Summary: unrefcount the symbol names when the CLD is destroyed

I was going to clean up the sometimes null value of _name and 
_name_and_id, and have the boot classloader data have a name, but 
there's a bootstrapping problem.  NULL CLD is created before the 
SymbolTable.  So this wasn't done.

Tested with mach5 hs-tier1-3, and runThese jck which does a lot of class 
unloading.

open webrev at http://cr.openjdk.java.net/~coleenp/8210559.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8210559

Thanks,
Coleen