I tried the solution here but I get the same error as the original error, also while exeucting it.
$ sudo ppa-purge ppa:chris-lea/zeromq
Updating packages lists
W: The repository 'http://ppa.launchpad.net/chris-lea/zeromq/ubuntu xenial Release' does not have a Release file.
What might it be?
apt-get update
stops complaining.apt-add-repository
or by manually editing your sources - see How to remove a particular PPA?. Since the PPA doesn't provide packages for your release, it should not have installed anything.