I have some SD cards with an EFI partition which I cannot use in my 3D printer. To get rid of the EFI partition you need to format the SD card with a MBRformat parameter. First use diskutil to find your disk position.
diskutil list
diskutil eraseDisk MS-DOS FAT32 MBRformat /dev/disk2
And afterwards if you check again with
diskutil list
You will see that the EFI partition is gone.