Docs: Remove duplicate text for is_main_site() parameter.

Props Kenshino.
Fixes #37241.


git-svn-id: https://develop.svn.wordpress.org/trunk@37932 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -4233,7 +4233,6 @@ function wp_suspend_cache_invalidation( $suspend = true ) {
  * @global object $current_site
  *
  * @param int $site_id Optional. Site ID to test. Defaults to current site.
- *                     Defaults to current site.
  * @return bool True if $site_id is the main site of the network, or if not
  *              running Multisite.
  */