I moved your thread to a more appropriate forum.
To answer your question, I don't know if I have ever bothered to convert any files that included a subtitle with it. If they were included with the original, I just didn't copy them over. However in looking, I may have found where you can remove them. I am not 100% sure about it though, perhaps one of our other members has dealt with this and can offer more insight, but I will share with you what I think.