TDML Runner - Infoset.contents is stripping off all attributes

The TDML runner removes all attributes from the Infoset XML that it pulls in from the TDML file. This can result in unparser errors due to loss of namespace bindings.

The Infoset.contents call redundantly calls the utility to remove attributes more than once.

This needs to be cleaned up and is related to DFDL-1384.