Doc: remove \instantiates commands

These QML types do not instantiate C++ classes.

Change-Id: Idd43012b5bf7c5d8d032befbaa1417329e014d8a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>