Comment 2 for bug 1923080

I assume that the message that you are missing should read

    This was likely caused by:
    Unofficial software packages not provided by Ubuntu
    Please use the tool 'ppa-purge' from the ppa-purge
    package to remove software from a Launchpad PPA and
    try the upgrade again.

This is the case on your system. You have added software from outside Ubuntu, namely the oibaf PPA.