avahi: remove rfb announce file

Remove uninstalled (?) VNC service announcement file.

Anyway, this file wasn't being installed because the action in https://github.com/XSCE/xsce/blob/71aef1/roles/common/tasks/avahi.yml#L19 lacks a `- name: bla bla` line.

Please, @scollazo and @jvonau take a look.