Don't change edited transclusion nodes to <span>s

This is harmful because we don't know whether <span> is acceptable
in context. They're not allowed in <tbody> for instance, and so if
we replace a <tr> with a <span> that breaks things.

Instead, use the nodeName of the first original DOM element.

Change-Id: I95ea9f13985767123f692706c6cc71fefd74d517
Merge "Don't change edited transclusion nodes to <span>s"