It is not a track frame but a road bike that has been converted into a single speed. The thing you were asking about is indeed a chain tensioner, and you can't just remove it because it is likely that the chain won't mesh up with both gears at the exact position of the rear dropout. If you wanted to remove it you would have to find a magic gear ratio that works with that distance and thus would have to try a bunch of different chainring/cog combinations and then you couldn't change them. Without doing this, the bike can only ever be a singlespeed and cannot ride as a fixed gear. I would pass.
People usually put these things here:http://www.bikeforums.net/showthread...list-eBay-find
It is kind of a catch all thread for people both considering a purchase or people who find things that they think other forum members might be interested or for things that are just really weird on craigslist.