unix/mpconfigport.h: Don't define MICROPY_ERROR_PRINTER, use standard one.
And standard one uses sys.stderr, not raw system stderr. (So now it can
be properly redirected, etc.)
// names in exception messages (may require more RAM).
#define MICROPY_ERROR_REPORTING (MICROPY_ERROR_REPORTING_DETAILED)
#define MICROPY_WARNINGS (1)
-#define MICROPY_ERROR_PRINTER (&mp_stderr_print)
#define MICROPY_PY_STR_BYTES_CMP_WARN (1)
extern const struct _mp_print_t mp_stderr_print;
