sys/pthread: deduplicate pthread group definition
sys/pthread: deduplicate pthread group definition

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