Remove font.c code commented out for a decade

Remove font.c code commented out for a decade

* src/font.c (LSTRING_HEADER_SIZE, LSTRING_GLYPH_SIZE, check_gstring)
(check_otf_features, otf_list, otf_tag_symbol, otf_open)
(font_otf_capability, generate_otf_features)
(font_otf_DeviceTable, font_otf_ValueRecord)
(font_otf_Anchor, Ffont_drive_otf, Ffont_otf_alternates)
(Fdraw_string, syms_of_font): Remove "experimental and not
tested much" code that has been "#if 0"-ed out for more than a
decade and which was getting in the way of maintenance.