Doc: Cleaned up information about SQL support.

-the list in the "Data Storage" is not aware that the items in the
 list are chapters in "SQL Programming" guide.
-removed extra list items to better give directions to readers.

Change-Id: I003132ea1038010e03aca0970d9683437b900e16
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Nico Vertriest <nico.vertriest@digia.com>
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>