Remove Role::addRestriction()

Method is not used.

refs #10887

library/Icinga/Authentication/Role.php

@@ -85,23 +85,6 @@ class Role
         return $this;
     }
 
-    /**
-     * Add a restriction to the role
-     *
-     * @param   string  $name
-     * @param   string  $restriction
-     *
-     * @return  $this
-     */
-    public function addRestriction($name, $restriction)
-    {
-        if (! isset($this->restrictions[$name])) {
-            $this->restrictions[$name] = array();
-        }
-        $this->restrictions[$name][] = $restriction;
-        return $this;
-    }
-
     /**
      * Get the restrictions of the role
      *