ssl_version_num is not used anymore

docs/libcurl/curl_version_info.3

@@ -34,7 +34,7 @@ typedef struct {
   const char *host;         /* human readable string */
   int features;             /* bitmask, see below */
   char *ssl_version;        /* human readable string */
-  long ssl_version_num;     /* number */
+  long ssl_version_num;     /* not used, always zero */
   const char *libz_version; /* human readable string */
   const char **protocols;   /* list of protocols */