Clean up custom fields view for radio and checkbox types for Activities

We need to apply the same changes for viewing radio and checkbox fields which extend 'Activities' as we applied to custom data fields which extend 'Contact'.

Currently, if you add a custom data group which extends Activiites and add a checkbox field to it, the display (view action) shows all options w/ frozen checkboxes.

Example URL on my local sandbox: http://localhost/dgg/drupal/civicrm/contact/view/activity?activity_id=4&action=view&id=1&cid=85&history=0