Drop nonsense comments about RootNode.

That subject has more to do with SerializableNode.  Which also might
not be the name we end up with for that.  ID'able Node?  LinkableNode?
Signed-off-by: Eric Myhre <hash@exultant.us>

node.go

@@ -6,12 +6,6 @@ type Node interface {
 	// GetField resolves a path in the the object and returns
 	// either a primitive (e.g. string, int, etc), a link (type CID),
 	// or another Node.
-	//
-	// If a Node is returned, it will be a unrooted node -- that is,
-	// it can be used to view the fields below it, but since it was not
-	// originally stored as a full node, you cannot immediately take
-	// a link to it for embedding in other objects (you'd have to make
-	// a new RootNode with the same content first, then store that).
 	TraverseField(path string) (Node, error)
 
 	// GetIndex is the equivalent of GetField but for indexing into an array