private void symbolRemoved(ProgramChangeRecord rec) {
		Address removeAddr = rec.getStart();
		Long symbolID = (Long) rec.getNewValue();
		domainObjectWorker.schedule(new SymbolRemovedJob(currentProgram, removeAddr, symbolID));
	}
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