Remove recent new marker macroPROXY_HOOK_NON_LINKED

and instead use PROXY_DECLARE_OPTIONAL_HOOK which
is defined to be equal to APR_DECLARE_EXTERNAL_HOOK.

Correct explanation for the use of
PROXY_DECLARE_OPTIONAL_HOOK.

Use PROXY_DECLARE_OPTIONAL_HOOK for the correct
hooks.

Adjust build/make_nw_export.awk to match the new
PROXY_DECLARE_OPTIONAL_HOOK.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1728663 13f79535-47bb-0310-9956-ffa450edef68