Update ass_set_fonts_dir documentation
Update ass_set_fonts_dir documentation

Now that libass never extracts fonts anymore, update documentation
accordingly.

astiob/libass,torque/libass,astiob/libass,asimonov-im/libass,grigorig/libass,tgoyne/libass,richardpl/libass,blinkseb/libass,tgoyne/libass,blinkseb/libass,xbmc/libass,tgoyne/libass,Distrotech/libass,vault/libass,stps/libass,Akemi/libass,mwgoldsmith/libass,torque/libass,libass/libass,xbmc/libass,Akemi/libass,blinkseb/libass,mwgoldsmith/libass,MrSmile/libass,Distrotech/libass,torque/libass,rhlee/libass,libass/libass,rhlee/libass,richardpl/libass,Akemi/libass,rhlee/libass,asimonov-im/libass,pigoz/libass-ct,vault/libass,pigoz/libass-ct,Distrotech/libass,pigoz/libass-ct,ShiftMediaProject/libass,richardpl/libass,MrSmile/libass,sanyaade-g2g-repos/libass,sanyaade-g2g-repos/libass,sanyaade-g2g-repos/libass,grigorig/libass,ShiftMediaProject/libass,mwgoldsmith/libass,stps/libass,stps/libass