You can't really get rid of the folders, but you could put whatever brushes you like into one folder.
You can move all the brushes out of the folders, however if you save the brush set and reopen it, the brushes will be in a folder.
You can mimic the view as in your screenshot by going to the Brush picker fly-out menu and checking Brush Tip and unchecking Brush Name and Brush Stroke and then adjusting the Size slider at the bottom of the Brush picker.