Fix memory leak in qMRMLTreeView.

vtkCollection and vtkCollectionIterator were being leaked.

do not backport to Slicer. It has already been fixed there.
ENH: Dynamically populate top-level module categories
COMP: Fix Slicer_QTSCRIPTEDMODULES_DISABLED
ENH: Expose qMRMLCheckableNodeComboBox API to python
Fix refresh frame problem on Windows
Restore icon on checkboxes
Fix Models crash on armature files

There is a bug in the ctkVTKDataSetModel used by that combobox. It is
assumed that all the arrays given are vtkDataArray. This is not necessarily
true (the vtkStringArray aren't for example). A crash occurs if array that
isn't a vtkDataArray is is present in the polydata.
However, this scenario is only allowed because the filter had the option
NoAttribute allowed. Otherwise the array types are checked and a null array
doesn't filter through.

Here we fix the symptom by removing the NoAttribute from the possible
options. Fixing the actual issue would require to change the code in CTK.