Remove unused `positioning` in `Table` component

[nsenave]

The Table component has a positioning property that is unused in Lunatic (it is not present in Lunatic's questionnaire json schema):

https://github.com/InseeFr/Lunatic/blob/9026d46c17a069caf5f4e3e7a64e37f94b804d62/lunatic-schema.json

This unused property should be removed.

[nsenave]

To do in a later release: remove this attribute completely.