boards/stm32f769i-disco: deduplicate doxygen group definition
boards/stm32f769i-disco: deduplicate doxygen group definition

The group is already defined in the doc.txt file so no need to define it again in board.h

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