Remove DL0 specific code from ipa_replica_install in ipaserver/install
    
    Replica files are DL0 specific therefore the knob extension for
    replica_file has been removed. Also the code that is only executed if
    replica_file is not None.
    
    The new variable replica_install has been added which is used in
    ServerInstallInterface.__init__
    
    See: https://pagure.io/freeipa/issue/7689
    Signed-off-by: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>