Remove obsolete comment about POSIX 1003.2/D11.2.

Remove obsolete comment about POSIX 1003.2/D11.2.
The current standard (POSIX 1003.1-2004) is correct.
(crc_remainder) [defined CRCTAB]: Renamed from "remainder" to avoid
collision with builtin function.
(main) [defined CRCTAB]: Output in lowercase hexadecimal, and
output the first 0 as 8 digits, to make it easier to compare to
the text of the standard.  Output crctab to be a const array.
(crctab): Use result of above changes.
(long_options): Remove; not needed if empty.
(main): getopt_long can't return 0 here, so simplify the code.