(detected_mask): Delete unused variable.

(detected_mask): Delete unused variable.
(decode_coding_iso_2022): Pay attention to the byte sequence of
CTEXT extended segment, and retain those bytes as is.
(decode_coding_ccl): Delete unused variable `valids'.
(setup_coding_system): Delete unused variable `category'.
(consume_chars): Delete unused variable `category'.  Make it work
for non-multibyte case.
(make_conversion_work_buffer): Argument changed.
(saved_coding): Delete unused variable.
(code_conversion_restore): Don't check saved_coding->destination.
(code_conversion_save): New function.
(decode_coding_gap, encode_coding_gap): Call code_conversion_save
instead of record_unwind_protect.
(decode_coding_object, encode_coding_object): Likewise.  Recover
PT.
(detect_coding_system): Delete unused variable `mask'.
(Fdefine_coding_system_internal): Delete unsed vaiable id;