+++ This bug was initially created as a clone of Bug #1206924

In bug 1206924 comment 7 we stumbled over the topic of public GPG signing keys
not being removed by zypper when invoking `zypper rr` and a related signing
key is no longer needed.

The opi package manages third party repositories and hit the problem of
properly cleaning up behind itself when repositories are deleted again. Having
third party GPG keys lingering in the rpmdb can be security relevant. In opi
this is now solved on foot for the time being.

So the question is whether it is possible to handle this on Zypper level
already to remove no longer needed keys from the rpmdb.