Remove DL0 specific code from __init__ in ipaserver/install/server
    
    The methods _is_promote has been removed from all classes as this has only
    been used internally to check if the domain level is correct.
    
    The check if the installer object has the attribute replica_file has been
    modified to use the new variable replica_install defined in
    CompatServerReplicaInstall instead.
    
    The DL0 specific code from ServerInstallInterface.__init__ has been removed
    
    See: https://pagure.io/freeipa/issue/7689
    Signed-off-by: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>