Now that we have a different ui for simple vs reference keyword, cardinality on
keyword reference is no more meaningful and hidden in the UI, since we would
like to always have cardinality=1 for reference keyword when generating profiles.

The easiest way to do so is to set proper default value, else by removing the
attribute we would have to do extra customization to the SEDA 2 profile
generator to consider that it shouldn't use the cardinality in the SEDA 2 XSD
(0..1).

Closes #16070921