Coverity CID 1241957. Removed the unused argument. As this struct and
pointer now are used only for krb5, there's no need to keep unused
function arguments around.
I brought back security.h in commit bb55293313. As we actually
already found out back in 2005 in commit 62970da675, the file name
security.h causes problems so I renamed it curl_sec.h instead.
