There are several open questions regarding older Ubuntu versions but none provide a working answer. Here are the steps I tried:
- I disabled discovery in cups-browsed configuration
- I disabled the whole service
- I removed the service
- I completely disabled avahi.
The last step worked but as I'm using avahi for other network discovery services, I don't want to remove it. Steps 1-3 work in CUPS itself, somehow Gnome is adding the printers, though. So what I'm looking for is the Gnome setting to disable printer discovery.