Edit Multiple: Remove option for removing co-creators

1. Log in

2. Post a work with another user as co-creator

3. Go to the mass edit page

4. Select said work for editing

On the mass edit page, there's a list of Current Authors and checkboxes you can check to remove. It's broken and we want to get rid of this ability.

To allow you to change which of your own pseuds you're using on the work, we'll need to add a Creator/Pseud(s) multiselect like the one that appears on the edit page for single works.

If this is done before we change the co-creator system to use invitations, deselecting all pseuds in the multiselect should remove you as co-creator. If it's done after, we might need to do something different to allow you to remove yourself.