MarkerSetImpl getByName(String name) {
			for (MarkerSetImpl set : markerSets) {
				if (name.equals(set.getName())) {
					return set;
				}
			}
			return null;
		}
Use this close listener approach instead of plugin events, since we don't get a
ProgramClosedPluginEvent when a trace view is closed, but we can listen for its
domain object closing, which works for plain programs, too.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/marker/MarkerManager.java