boards/nucleo-l552ze-q: remove PLL N custom define
boards/nucleo-l552ze-q: remove PLL N custom define

OTAkeys/RIOT,ant9000/RIOT,authmillenon/RIOT,miri64/RIOT,miri64/RIOT,ant9000/RIOT,ant9000/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,kaspar030/RIOT,kaspar030/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,authmillenon/RIOT,authmillenon/RIOT,ant9000/RIOT,kaspar030/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,miri64/RIOT,OlegHahm/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,miri64/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,ant9000/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,jasonatran/RIOT,kaspar030/RIOT,jasonatran/RIOT