Code maintenance follow up to r61179. Move `wp_new_comment_via_rest_notify_postauthor` callback from REST API Comments controller to comment.php. Add default to `wp_notes_notify` for multisite compatibility. Props adamsilverstein, justlevine, mukesh27, mamaduka, peterwilsoncc, desros. See #64204. Built from https://develop.svn.wordpress.org/trunk@61199 git-svn-id: http://core.svn.wordpress.org/trunk@60535 1a063a9b-81f0-0310-95a4-ce76da25c4cd