We removed these pretty quickly!!!!
We tried prying, banging these with a sledge hammer, getting to the nuts underneath, using an Allen wrench and drill attachment, drilling through with cobalt drill bits, using a diamond blade on an angle grinder, and yelling at these things. The angle grinder was minimally useful, but the others didn't work. On a whim, we just got my circular saw out with a Diablo demolition/wood blade on it. We made a cut across every Allen bolt head and perpendicular to the rail (which is every 4 inches). Each cut last about 3 seconds... and you just go through the metal. After that, you bang out the 4" sections with a hammer. We ground off the heads with our angle grinder and punched them through the floor. Basically, it took us about an hour for a 16' section of rail... start to finish. Hope this helps! Good luck, everyone.