* coding.h (struct coding_system): Remove 'error_positions' (unused)

* coding.h (struct coding_system): Remove 'error_positions' (unused)
and 'errors' (set but unused) fields.  Use bitfields for 'eol_seen',
'mode', 'common_flags' and 'result' fields, adjust layout to avoid
extra padding and shrink struct coding_system by 56 bytes (x86_64).
* coding.c (decode_coding_utf_8, decode_coding_utf_16)
(decode_coding_emacs_mule, decode_coding_iso_2022, decode_coding_sjis)
(decode_coding_big5, decode_coding_charset, decode_coding)
(encode_coding): Adjust users.