Clean up c2x code-path by not double-setting the prefix variable.

* server/util.c
  (c2x): Take a new prefix parameter instead of hard-coding '%' and then
  conditionally setting 'x' for half of the cases.

Reviewed by: nd


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@292111 13f79535-47bb-0310-9956-ffa450edef68