DeadServer cleanup

Cleanup of DeadServer class shutting down access, undoing duplication, adding doc., and removing unused code.

One change is that we do not remove a server from 'processing' list when we 'remove' deadservers; we let SCP do it since it owns processing list (Saw issue where on fast restart of a server, the server was removed from deadserver and from processing list though the SCP for the dead server was still running – no repercussions that I could see but a little confusing).