Monitor: Remove ping infrastructure
    
    Now thast services use an internal watchdog we do not need pings anymore,
    this will cut down the chatter and allow more flexible process management,
    for example socket activation and exit-on-idle.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2921
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>