Amend Figshare `clean_up` function to properly handle published items

[rhigman]

Currently this function simply attempts to delete the relevant project. As noted in the comments:

thoth-dissemination/fsuploader.py

Line 480 in bdb5a35

This will fail if the project or any of its articles is already published.

Now that automatic publication (i.e. without manual approval) has been enabled on Loughborough Figshare, the plain delete is no longer sufficient, because the cleanup may be requested at a point where one or more articles within the project has already been made public.