Simply deleting the field from the ACF admin does not delete the meta data from the post. Try recreating the field ( be sure its the same field name) and go into the post and empty the fields value, save the changes, THEN go and delete the ACF field. Now you’ll have an empty meta value in the post and nothing should appear in the posts frontend + no more field.
Another way to do it would be to delete the meta value directly in the wp_postmeta table but I’m assuming you prefer not to tamper with that 🙂
