Remove phpdoc return type of null for preg_replace

lib/special_cases.php

@@ -139,15 +139,14 @@ function apcu_fetch($key)
  * -1 (no limit).
  * @param int $count If specified, this variable will be filled with the number of
  * replacements done.
- * @return string|array|null preg_replace returns an array if the
+ * @return string|array preg_replace returns an array if the
  * subject parameter is an array, or a string
  * otherwise.
  *
  * If matches are found, the new subject will
  * be returned, otherwise subject will be
  * returned unchanged.
  *
- * Returns a file pointer resource on success, .
  * @throws PcreException
  *
  */