sys/arduino/doc: Removed SPI from ToDo
sys/arduino/doc: Removed SPI from ToDo

The SPI interface has been added, so it should no longer be listed on the ToDo
list.

kaspar030/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,mtausig/RIOT,smlng/RIOT,toonst/RIOT,smlng/RIOT,toonst/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,aeneby/RIOT,authmillenon/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,ant9000/RIOT,yogo1212/RIOT,miri64/RIOT,miri64/RIOT,x3ro/RIOT,mtausig/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,x3ro/RIOT,kaspar030/RIOT,kaspar030/RIOT,miri64/RIOT,miri64/RIOT,yogo1212/RIOT,josephnoir/RIOT,basilfx/RIOT,ant9000/RIOT,kYc0o/RIOT,OlegHahm/RIOT,kYc0o/RIOT,mtausig/RIOT,mtausig/RIOT,basilfx/RIOT,miri64/RIOT,aeneby/RIOT,josephnoir/RIOT,yogo1212/RIOT,yogo1212/RIOT,kYc0o/RIOT,yogo1212/RIOT,josephnoir/RIOT,yogo1212/RIOT,smlng/RIOT,OTAkeys/RIOT,toonst/RIOT,aeneby/RIOT,basilfx/RIOT,RIOT-OS/RIOT,toonst/RIOT,x3ro/RIOT,authmillenon/RIOT,ant9000/RIOT,authmillenon/RIOT,x3ro/RIOT,smlng/RIOT,mtausig/RIOT,jasonatran/RIOT,authmillenon/RIOT,toonst/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,aeneby/RIOT,x3ro/RIOT,josephnoir/RIOT,OlegHahm/RIOT,basilfx/RIOT,smlng/RIOT,ant9000/RIOT,kaspar030/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,josephnoir/RIOT,aeneby/RIOT,basilfx/RIOT,kYc0o/RIOT