removed obsolete require_once('config.php') from recaptcha-bp plugin

the configuration directive has been moved to wp-config.php, so it was
duplicated. Should solve part of
https://git.autistici.org/ai/noblogs-wp/issues/13

wp-content/plugins/wp-recaptcha-bp/recaptcha.php

@@ -11,7 +11,6 @@
  * @link      http://www.google.com/recaptcha
  */
 
-require_once('config.php');
 require_once('wp-plugin.php');
 
 if (class_exists('ReCAPTCHAPlugin'))