Mitchell, unless you're truly obsessive about it, there's really no need to do that. A history state in Lr takes very little storage space. It's not like in PS where massive amounts of pixel data are stored for each history step.
If you really want to remove it, the only way I'm aware of (that's not to say there might not be an easier way), is to make sure to write the image metadata with Ctrl-S, 'remove' the image from the catalog, and then reimport the image. Along with the history steps, you will also lose Collection membership, Virtual Copies, Stacks, and Pick Flags for that image.