Inline the proxy availability check because the existence of the function

is_proxy_available() is historical and from days where no find_linked_module()
function existed and where this was a bigger function.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80433 13f79535-47bb-0310-9956-ffa450edef68