PCTLIBRARY-1211 Only remove listeners on SelectionField options property

 - Removing listeners on SelectionField properties value, enabled, visible was unnecessary because they are instances of Property and were already being removed by removeChildListeners
 - options property is a NodeList, not a Property, so it doesn't get put in the list of Properties by PresentationNode.properties()

Also adds missing AT test file for the ExtJsComboBoxControl.

(@jeremyh, @janh)