axe an unnecessary call to sscanf() when parsing the response line

from the origin server

apr_date_checkmask() already verified the expected text and digit
positions; all that is needed is to cheaply find which digits


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@999694 13f79535-47bb-0310-9956-ffa450edef68