Gutenberg does not use the remove_meta_box command

I was testing Gutenberg a bit today and I noticed that the default author dropdown appears in the Document panel even when Co-Authors-Plus is active.

Of course currently [this command](https://github.com/Automattic/Co-Authors-Plus/blob/master/co-authors-plus.php#L325) removes the box from the classic editor.

I've been looking around for what the equivalent is in Gutenberg. Most of the support threads I've seen end up pointing me to this [GitHub issue](https://github.com/WordPress/gutenberg/issues/6533), which started out specific to featured images, but also mentions others (such as in [this comment](https://github.com/WordPress/gutenberg/issues/6533#issuecomment-401137263)).

While this issue is not closed in Gutenberg, I thought it would be good to flag it here in case they come up with a usable solution before launch that can be implemented here.

Start with co-authors-plus.php around line 325 and review Gutenberg issue 6533 for the supported equivalent of remove_meta_box. Confirm whether Gutenberg now exposes a usable way to remove the default author dropdown from the Document panel when Co-Authors-Plus is active; done means the dropdown is no longer shown in that setup.

Written by the indexing model from the issue text.