9a001381 (Fix tests under GETTEXT_POISON on parseopt, 2012-08-27)
introduced check_i18n, but the helper was never used from the
beginning.
The same commit also introduced check_unknown_i18n to replace the
helper check_unknown and changed all users of the latter to use the
former, but failed to remove check_unknown itself.
Signed-off-by: Junio C Hamano <gitster@pobox.com>