Get rid of the 'keepalive' pinger since no longer needed

AFAICS, I don't think there is a need for the keep alive pinger any more. It can happen that an http session of a website in the channel mgr gets a timeout (for example a website loaded over /site), but after that, the next request will just do a new SSO and should render the site again.

IIRC, it was really needed for the 'rest RPC' calls over _rp and _targeting for example, but those requests now always hit the cms webapp.

Hence, AFAIK, we should be able to completely drop the keep alive pingers for all website webapps.