ipatests: remove wrong job definition TestACMEPrune
    
    In ipa-4-9 branch, there is no TestACMEPrune in the
    test test_integration/test_acme.py.
    The nightly job was introduced by mistake by a
    backport. Remove the nightly job definition.
    
    Related: https://pagure.io/freeipa/issue/9324
    
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Michal Polovka <mpolovka@redhat.com>