Throughout the file, delete all USE_FONT_BACKEND

Throughout the file, delete all USE_FONT_BACKEND
conditionals.  Don't check enable_font_backend.  Delete all codes
used only when USE_FONT_BACKEND is not defined.
(xic_create_xfontset): Original code deleted and renamed from
xic_create_xfontset2.  Use FRAME_FONT, not FRAME_FONT_OBJECT.
(x_make_gc): Don't set GCFont in GCs.
(Fx_create_frame) [USE_LUCID]: Set xlwmenu_default_font to a font
opened by "fixed".
(syms_of_xfns): Don't set get_font_info_func, load_font_func,
find_ccl_program_func, query_font_func, set_frame_fontset_func,
get_font_repertory_func.