Hard to know what will happen if you remove the line of stitching on the outside. I was taught to put the steeking invisibly on the inside, and it's rare to see a hand sewn kilt with the steeking on the outside. But steeking has a purpose, and it helps stabilize the pleats at the bottom of the fell. Removing yours might not be a good idea. I think I'd just leave it and consider it a part of the kilt as it was made by the kiltmaker.