Docs: Revert documentation change for `wp_get_attachment_metadata()`.

This more accurately describes the behavior of the function, and is more consistent with the documentation for other post and attachment functions.

Follow-up to [50039].

Props Mista-Flo.
Merges [50051] to the 5.6 branch.
See #52196.
Built from https://develop.svn.wordpress.org/branches/5.6@50052


git-svn-id: http://core.svn.wordpress.org/branches/5.6@49753 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/post.php

@@ -6071,7 +6071,7 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
  *
  * @since 2.1.0
  *
- * @param int  $attachment_id Attachment post ID. Default 0.
+ * @param int  $attachment_id Attachment post ID. Defaults to global $post.
  * @param bool $unfiltered    Optional. If true, filters are not run. Default false.
  * @return array|false {
  *     Attachment metadata. False on failure.

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6.1-alpha-50050';
+$wp_version = '5.6.1-alpha-50052';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.