private void referenceRemoved(ProgramChangeRecord rec) {
		Reference ref = (Reference) rec.getObject();
		domainObjectWorker.schedule(new ReferenceRemovedJob(currentProgram, ref));
	}
Tells a plugin that it is no longer needed.
The plugin should remove itself from anything that
it is registered to and release any resources.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/symtable/SymbolTablePlugin.java