pkg/openthread: cleanup Makefile.dep
pkg/openthread: cleanup Makefile.dep

There's no need to load dependency modules if the package is used. This is already managed by the build system

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