Keep directory listing compile-time option

src/http.h

@@ -26,7 +26,6 @@ struct mg_http_serve_opts {
   const char *root_dir;        // Web root directory, must be non-NULL
   const char *ssi_pattern;     // SSI file name pattern, e.g. #.shtml
   const char *extra_headers;   // Extra HTTP headers to add in responses
-  const char *enable_dirlist;  // Enable dir listing. Set to "no" to disable
 };
 
 // Parameter for mg_http_next_multipart