(LEADING_BYTE_*): Delete definition for non-UTF-2000.

(LEADING_BYTE_PRIVATE_P): Deleted unconditionally.
(LEADING_BYTE_PREFIX_P): Deleted.
(PRIVATE_LEADING_BYTE_PREFIX): Deleted.
(BUFBYTE_FIRST_BYTE_P): Delete definition for non-UTF-2000.
(BUFBYTE_LEADING_BYTE_P): Deleted.
(CHARSET_PRIVATE_P): Deleted unconditionally.
(rep_bytes_by_first_byte): Deleted unconditionally.
(REP_BYTES_BY_FIRST_BYTE): Delete definition for non-UTF-2000.
(FIELD1_TO_PRIVATE_LEADING_BYTE): Likewise.
(FIELD1_TO_OFFICIAL_LEADING_BYTE): Likewise.
(FIELD2_TO_PRIVATE_LEADING_BYTE): Likewise.
(CHAR_FIELD2): Deleted.
(CHAR_FIELD3): Deleted.
(MAKE_CHAR): Delete definition for non-UTF-2000.
(BREAKUP_CHAR_1_UNSAFE): Deleted.
(breakup_char_1): New implementation.
(CHAR_CHARSET): Use `BREAKUP_CHAR'.
(CHAR_LEADING_BYTE): Use `CHAR_CHARSET'.