Remove leftover table unibyte_to_multibyte_table.

Remove leftover table unibyte_to_multibyte_table.
* character.c (unibyte_to_multibyte_table): Remove.
(Funibyte_char_to_multibyte): Use MAKE_CHAR_MULTIBYTE.
* charset.c (init_charset_once): Don't init unibyte_to_multibyte_table.
* character.h (UNIBYTE_TO_CHAR): New macro.
(MAKE_CHAR_MULTIBYTE): Use it.
(unibyte_to_multibyte_table, unibyte_char_to_multibyte): Remove.
* xdisp.c (get_next_display_element): USE ASCII_CHAR_P.
(message_dolog, set_message_1):
* search.c (Freplace_match):
* editfns.c (Fcompare_buffer_substrings):
* fns.c (Fcompare_strings): Use MAKE_CHAR_MULTIBYTE.
(concat):
* insdel.c (copy_text, count_size_as_multibyte):
Use ASCII_CHAR_P and BYTE8_TO_CHAR.
* term.c (produce_glyphs):
* syntax.c (skip_chars): Use BYTE8_TO_CHAR.
* regex.c (RE_CHAR_TO_MULTIBYTE):
* cmds.c (internal_self_insert):
* buffer.h (FETCH_CHAR_AS_MULTIBYTE): Use UNIBYTE_TO_CHAR.