RFR (XS) 8209738: Remove ClassLoaderDataGraph::*oops_do functions

[coleen.phillimore at oracle.com]

Summary: Make walking CLDG more consistent.

Affects ParallelGC and jvmtiTagMap.

open webrev at http://cr.openjdk.java.net/~coleenp/8209738.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8209738

Tested with mach5 tier1-7 and with runThese with all GCs.

Thanks,
Coleen