Remove apr_strnatcmp.h. All of the functions prototyped in this file

have been moved to apr_strings.h.  This also modifes Apache to include
apr_strings.h instead of apr_strnatcmp.h


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85872 13f79535-47bb-0310-9956-ffa450edef68