Removing doubled description tab in template styles

Same as PR #2685 but against staging and same as PR #2481, but for template styles.

To test you can create a fieldset named "description" in the templateDetails.xml and add a field to it. The tab will show up twice.
Apply patch and it will show up only once.

Tracker: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32957

#### Comment by JM on Original PR
> When one creates such a description fieldset:
If the template xml description is long, we then get in the details Tab a link to "Show full description".
Clicking on that link then loads the Description Tab which may contain fields unrelated to the `<description>` in the xml.
Also, forgot to say that the long description is fully displayed in the Details tab.