Replace is_callable checks with type hints

Also removes tests checking the exceptions thrown from
the removed is_callable checks.

Author: mpajunen

Normalizer/AbstractNormalizer.php

@@ -86,15 +86,9 @@ public function setCircularReferenceLimit($circularReferenceLimit)
      * @param callable $circularReferenceHandler
      *
      * @return self
-     *
-     * @throws InvalidArgumentException
      */
-    public function setCircularReferenceHandler($circularReferenceHandler)
+    public function setCircularReferenceHandler(callable $circularReferenceHandler)
     {
-        if (!is_callable($circularReferenceHandler)) {
-            throw new InvalidArgumentException('The given circular reference handler is not callable.');
-        }
-
         $this->circularReferenceHandler = $circularReferenceHandler;
 
         return $this;