If you need to delete a Linux MBR, you can simply use the dd command, this might be more useful with a USB stick that still has an MBR.
WARNING!! Don’t so any of this if you don’t understand it or be careful not to mix your disk designations up i.e. /dev/sdb or /dev/sdc could be your real disk!
The following will delete the MBR on /dev/sdc:
dd if=/dev/zero of=/dev/sdc bs=446 count=1