drivers/Makefile.dep: remove useless FEATURES_PROVIDED for rtc_rtt
drivers/Makefile.dep: remove useless FEATURES_PROVIDED for rtc_rtt

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