2 hours times 3600 seconds per hour times 24 fps (assuming it is 24 and not 29.997) = 172800 frames. You will need to shop the subtitles out of roughly 172800 frames. Thankfully some frames won't have subtitles, so the work isn't really that much.
But seriously, unless the subtitles are part of a separate stream in the avi container, there is no easy way to take it out. You could try chroma keying it out, but it won't look that good.