What to do with the wires when removing baseboard heaters
The code is more concerned with wires you can access and remove. A good example would be a drop ceiling grid.  

In your case if you do not have that ability then yes just snipping off the wires will suffice.  As an extra precaution stager the cut ends and tape off the ends with electrical tape.  

Then remove them completely from the panel as to prevent any unforeseen reconnects.  If you are uncomfortable with working in your panel this way I would suggest hiring a licensed electrician.