Docs: Add missing parameter and return descriptions to the DocBlock for the deprecated `default_topic_count_text()`.

See #32246.


git-svn-id: https://develop.svn.wordpress.org/trunk@36760 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/deprecated.php

@@ -3382,6 +3382,9 @@ function rich_edit_exists() {
  * @since 2.7.0
  * @access private
  * @deprecated 3.9.0
+ *
+ * @param int $count Number of topics.
+ * @return int Number of topics.
  */
 function default_topic_count_text( $count ) {
 	return $count;