Status of removed service is shown

[Holundermann]

The status of a removed service is still shown in the webfrontend:

The mem service was removed and is not shown in icingaweb2 anymore but is still visible in the monitoring tab of foreman, icingweb2 view:

[dgoetz]

I thought about this for a while now and did not find a good and easy solution. There is no event we can get from Icinga 2 (or only for objects that are managed by api endpoints for single objects). The typically behavior is a reload of Icinga 2 and a object removed from configuration is gone, so I think the only way to solve this is handling it during the initial importer and do something like store the timestamp of the last initial import and invalidate all objects older than this timestamp.