protected synchronized void clearUndo() {
		undoList.clear();
		redoList.clear();

		// Flatten all checkpoints then restore undo stack size
		dbHandle.setMaxUndos(0);
		dbHandle.setMaxUndos(NUM_UNDOS);
	}
Clear undo/redo stack.
<br>
NOTE: It is important that this always be invoked following any save operation that 
compacts the checkpoints within the database {@link BufferMgr}.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/data/StandAloneDataTypeManager.java