@Override
	public void processEvent(PluginEvent event) {
		if (event instanceof ProgramClosedPluginEvent) {
			Program p = ((ProgramClosedPluginEvent) event).getProgram();
			editorMgr.programClosed(p);
		}
		super.processEvent(event);
	}
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/stackeditor/StackEditorManagerPlugin.java