dir.c: get rid of the wildcard symbol set in no_wildcard()

Elsewhere in this file is_glob_special() is also used to check for
wildcards, which is defined in ctype. Make no_wildcard() also use this
function (indirectly via simple_length())

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>