cksum: minor crctab generation cleanups

cksum: minor crctab generation cleanups

* src/cksum.c [CRCTAB]: Include only config.h and stdio.h,
to simplify the crctab-generating code.
[!CRCTAB]: Do not include stdint.h or stdio.h, as cksum.h does it now.
(BIT, r, crc_remainder, main) [CRCTAB]: Use unsigned int, not
uint_fast32_t or uint32_t, as this is good enough for GNU where
unsigned int is guaranteed to be at least 32 bits, and this way we
needn’t worry about mismatches between %08x formats and uint_fast32_t.
(main) [CRCTAB]: Prefer more-local decls.  Do not output
unnecessary directives to include stdint.h or stdio.h.
No need for ‘return EXIT_SUCCESS;’ nowadays.
* src/crctab.c: Regenerate.