Upon uninstalling qubes-contrib-rpm the key file would get removed, but
the key remain in the RPM database. This removes the key permanently.

Fixes QubesOS/qubes-issues#10310

Installing a qubes-contrib package immediately after adding the
repository via "qubes-repo-contrib" would fail. This was because the key
had not yet been imported and dom0 was discarding the package due to it
not being properly signed.

A shorter timeout increases the likelyhood that the key is already
available by the time the user attempts to make use of the newly added
qubes-contrib repository. This also adds the same logic key removal, but
the argument there is that the system could be shut down before the
systemd-run command had a chance to remove the key.

Fixes QubesOS/qubes-issues#10311

According to systemd.timer man page the default timer accuracy is 1
minute. This needed to be overridden to a value closer to our set delay
for it to more accurately trigger at the previously set --on-action=5s.