Low: pacemakerd: remove unneeded IPC and CPG commands
    
    Now that the controller handles crm_node's -l/-p needs, pacemakerd no longer
    needs to. Backward compatibility isn't an issue because pacemakerd IPC isn't
    proxied for Pacemaker Remote, so only local clients are relevant, and the
    pacemakerd IPC never had a C API, which means it was internal only.
    
    Without those commands, pacemakerd no longer needs to track a process mask,
    connect to CPG, or maintain the peer cache.
    
    The only remaining need for the cluster layer is to use corosync CFG to tell
    corosync to initiate or block shutdown.