Remove unused code in the reference processor

In JDK 7u2 the way the reference processor manages the pending list was changed. This was done as part of JDK-4965777. The code to support the old behavior is still there, but haven't been used for a long time and could be removed.

This basically means that code using ReferenceProcessor::pending_list_uses_discovered_field() should be cleaned up and ReferenceProcessor::pending_list_uses_discovered_field() should be removed. The following files are affected.

prims/jvm.h
runtime/java.hpp
runtime/java.cpp
oops/instanceRefKlass.cpp
memory/referenceProcessor.hpp
memory/referenceProcessor.cpp