Allow -exportsteadystate with MTBDD engine

Now that non-sparse StateValueMTBDD printing is working, we can remove
this restriction.

prism/src/prism/Prism.java

@@ -3367,9 +3367,6 @@ public class Prism extends PrismComponent implements PrismSettingsListener
 		// Do some checks
 		if (!(currentModelType == ModelType.CTMC || currentModelType == ModelType.DTMC))
 			throw new PrismException("Steady-state probabilities only computed for DTMCs/CTMCs");
-		if (fileOut != null && getEngine() == MTBDD)
-			// TODO: auto-switch?
-			throw new PrismException("Steady-state probability export not supported for MTBDD engine");
 		if (exportType == EXPORT_MRMC)
 			exportType = EXPORT_PLAIN; // no specific states format for MRMC
 		if (exportType == EXPORT_ROWS)