`$args` param in `get_coauthors()` is ignored

This was altered about a year ago in 2d8709bf30945fb407d85be72595b9d5128c016a, and it's interesting that it hasn't been caught. `wp_get_post_terms()` was replaced with `get_the_terms()`, but [`get_the_terms()`](https://github.com/WordPress/WordPress/blob/master/wp-includes/category-template.php#L1084-L1100) does not accept arguments.