[Matlab] Fix ThermoPhase 'clear' method

This function was actually being directed into 'thermoget' and calling the
'newFromXML' method (on a non-existent XML tree) instead of calling the 'del'
method.

interfaces/matlab/toolbox/@ThermoPhase/clear.m

@@ -6,5 +6,5 @@ function clear(tp)
 %     object that derives from ThermoPhase)
 %
 
-thermo_set(tp.tp_id, 0, 10);
+thermo_set(tp.tp_id, 10, 0);