Fix typo: this.transclusionNode -> this.selectedNode

this.transclusionNode doesn't exist. Also remove instanceof checks
as they are already done in #get(Selected|Reference)Node.

Bug: 64717
Change-Id: I7ff0133d1ad45edda8de2cbad459706dbaceb5f2
Merge "Fix typo: this.transclusionNode -> this.selectedNode"