beta: $wgSquidServers is no more needed

52818a3d configures HTCP multicast purging, that makes $wgSquidServers
obsolete so just get rid of it.

I also removed bits entirely, might look at it later on but it is
unneeded right now.

Change-Id: Iab0fd8b1133f2f7e0419d70f68e8d11d50d91925