Remove NixSpam from Rspamd configuration

[DavidePrincipi]

The NixSpam service has shut down and is now sending emails to users via abuse@.

Rspamd has already addressed this issue: rspamd/rspamd#5299.

Proposed actions

Update Rspamd container for NethServer 8 to remove NixSpam.

Alternatives

Wait for the upstream patch to be adopted by Alpine.

See also

https://mattermost.nethesis.it/nethesis/pl/eqdbb6dsf7rq5br8yhh7ngibma

[DavidePrincipi]

Test case

With Mail 1.5.3 the NIXSPAM symbols are visibile in Rspamd web UI.

After upgrading to the testing version they must not be listed any more.

[DavidePrincipi]

In testing 1.5.4-dev.1

See test case in the previous comment

[nrauso]

test case: VERIFIED