remove duplicate abstract function declaration

Author: FlorianLB

src/CleverAge/Ruler/RuleAbstract.php

@@ -54,11 +54,6 @@ abstract class RuleAbstract implements RuleInterface
      */
     protected $_nand_children = array();
 
-    /**
-     * {@inheritdoc}
-     */
-    abstract public function doIsSatisfied();
-
     /**
      * {@inheritdoc}
      */