You can undo the changes made by this app by installing and opening a terminal emulator (there are several on the market) and typing the following:
su
mount -o remount,rw /dev/block/mtdblock3 /system
rm /system/bin/su
rm /system/xbin/su
rmdir /system/xbin
mount -o remount,ro /dev/block/mtdblock3 /system
exit
exit
