I know that it is splitting hairs, but technically those are Huck bolts. If you look at the picture he posted of the back side of them, you can see the tooling marks from the tool used to install them. Check out the page below for videos on the differences in installation of Huck Bolts versus Huck rivets. Regardless, removal of them is essentially the same. The easiest way is to grind or cut off one side or the other, then use a hammer & punch to pop out the opposite side. With a center punch, a good quality (cobalt is best) drill bit, & plenty of care, it is possible to drill them out, but that is definitely the more difficult option for removing them.