remove fn_data from event handler signature

examples/file-upload-multiple-posts/main.c

@@ -6,7 +6,7 @@
 // HTTP request handler function. It implements the following endpoints:
 //   /upload - Saves the next file chunk
 //   all other URI - serves web_root/ directory
-static void cb(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+static void cb(struct mg_connection *c, int ev, void *ev_data) {
   if (ev == MG_EV_HTTP_MSG) {
     struct mg_http_message *hm = (struct mg_http_message *) ev_data;
     if (mg_http_match_uri(hm, "/upload")) {
@@ -25,7 +25,6 @@ static void cb(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
       mg_http_serve_dir(c, ev_data, &opts);
     }
   }
-  (void) fn_data;
 }
 
 int main(void) {