Is it possible to call a custom ajax event after removing a file from a managed_file field?
I tried to do the same in D7 a while ago and I discovered a JS only solution is not possible. You need to add an ajax command to the Drupal callback.
Here's a similar question to yours. This one is about the upload button and you want the remove button.
In D7, the upload and remove button were handled by the same function and when I look at the D8 class of the managed file I also see only one callback: uploadAjaxCallback. So it might be worth checking that out.