Hi,
Those to strips were stiffening ribs. According to my references ( Modlers Datafile - The Supermarine Spitfire - Volume 1 - Merlin powered by SAM and "Spitfire, The Canadians" by Robert Bracken, with the most accurate set of plans, so I've read) Some aircraft had them, some did not.
If you want to remove them I would suggest a chisel blade exacto and carefully remove them. I would be really careful as you don't want to dig into the wing. You could also use your sanding sticks and remove them that way. Starting with a heavy grit and working to a wet sand should do you the trick. I would then re-scribe the panel lines witha rescribing tool or a darning needle in a holder or the backside of an exacto blade. Lightly, and I mean lightly scribe the lines in by making several passes over the area ( using a ruler a a straightedge) to be scribed until you feel that you've reached the same depth.Smooth it out with scotchbrite or very fine steel wool, and your done.
I think I would leave'em on myself, its not incorrect to have them there, and easier, which means more time to build more!
Any other questions don't hesitate
Regards
Pete