[BUG] Date/time with 'enableTime=false' should save value in the submission data in the [YYYY]-[MM]-[DD] ISO-8601 format

[mpetit-boop]

Description

The solution provided in Issue #4178 no longer resolves the problem in version 6.0.1 of formio.js.

Steps to Reproduce

1. Make sure you're using v6.0.1.
2. Add a DateTime component. Uncheck the "Enable Time Input" option in the Time tab.
3. In the Data tab, apply the fix suggested in Issue [BUG] Date/time with 'enableTime=false' should save value in the submission data in the [YYYY]-[MM]-[DD] ISO-8601 format #4178, which is to add { "dateFormat": "yyyy-MM-dd" } in the Flatpickr options.

Expected Behavior

The fix in the related issue should still work, or this should have been fixed in releases following the related issue thread to avoid requiring this workaround.

Actual Behavior

The date time value is still saved in the submission data in an ISO format instead of [YYYY]-[MM]-[DD].