Duplicate results for Webform Likert and other multi-property elements.

When you add a webform likert field to a view, the join to the webform_submission table does not limit the results to just one row from each submission. If a likert has, say, 5 questions, then the view gets five rows. Adding "Distinct" to the view doesn't help: if you have 3 different answers, you get 3 rows of results.

For delta, this is handled in WebformSubmissionField::query() by adding delta = 0 to the query to prevent multi-answer items from causing the same problem. The following patch does the same for properties. It isn't actually necessary to return the data because it is submission entity is going to be created for display.