(font_score): Delete arg alternate_families. Check only

(font_score): Delete arg alternate_families.  Check only
weight, slant, width, and size.
(font_sort_entites): Adjusted for the above change.  Reflect the
order of font-driver to scores.
(font_list_entities): Don't check alternate_familes here.
(font_clear_prop): Handle foundry.
(font_update_lface): Don't parse "foundry-family" form here.
Handle FONT_FOUNDRY_INDEX.
(font_find_for_lface): Likewise.  Handle alternate families here.
(font_open_for_lface): Pay attention to size in ENTITY.
(font_open_by_name): Simplified by calling font_load_for_lface.
(free_font_driver_list): Delete it.
(font_update_drivers): Preserve the order of backends.
(syms_of_font): Setting of sort_shift_bits adjusted for the change
of font_score and font_sort_entites.