Revert r30115 which was a breaking change for code which interacts with the return value of `get_metadata()` when no meta key is specified.

See #15030


git-svn-id: https://develop.svn.wordpress.org/trunk@30701 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/meta.php

@@ -493,10 +493,6 @@ function get_metadata($meta_type, $object_id, $meta_key = '', $single = false) {
 	}
 
 	if ( ! $meta_key ) {
-		foreach ( $meta_cache as &$meta_values ) {
-			$meta_values = array_map( 'maybe_unserialize', $meta_values );
-		}
-
 		return $meta_cache;
 	}