server install: remove error log about missing bkup file
    
    The client installer code can be called in 3 different ways:
    - from ipa-client-install CLI
    - from ipa-replica-install CLI if the client is not already installed
    - from ipa-server-install
    
    In the last case, the client installer is called with
    options.on_master=True
    As a result, it's skipping the part that is creating the krb5
    configuration:
        if not options.on_master:
            nolog = tuple()
            configure_krb5_conf(...)
    
    The configure_krb5_conf method is the place where the krb5.conf file is
    backup'ed with the extention ".ipabkp". For a master installation, this
    code is not called and the ipabkp file does not exist => delete raises
    an error.
    
    When delete fails because the file does not exist, no need to log an
    error message.
    
    Fixes: https://pagure.io/freeipa/issue/9306
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>