@Override
	public void addGraphChangeListener(VisualGraphChangeListener<V, E> l) {
		changeListeners.add(l);
	}
Called after one or more vertices have been removed.  The callback will happen after
all removals have taken place.  This is an extension point for subclasses.

@param removed the removed vertices
Ghidra/Framework/Graph/src/main/java/ghidra/graph/graphs/DefaultVisualGraph.java