Remove restarted_named and xfail
    
    With shorter TTL, several named restarts are no longer necessary to make
    tests pass. The test case TestZoneSigningWithoutNamedRestart is no
    longer relevant, too.
    
    Modification of the root zone and disabling/enabling signing still seems
    to need a restart. I have marked those cases as TODO.
    
    See: https://pagure.io/freeipa/issue/5348
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>