empty namespace delcarations in examples

[sydb]

[Note — this may not be a bug, but we do not have a label for “investigate to see if this is a bug or not”.]
There are 18 cases of xmlns="" in the Guidelines. 11 of those are in SG, and thus are probably appropriate. (But I have not looked.) @hcayless and I (who are sitting at a gate at EZE) have not figured out why they are there.
They do not show up in the HTML output. The main effect, as far as I can think at the moment, would be to make it hard for us to find those constructs using XPath (since we would be searching for teix:whatever', not whatever` in no namespace.) But they me be there in some attempt to avoid validation?
So this ticket is to remind us that there is a potential problem.

Source/Guidelines/en/AI-AnalyticMechanisms.xml:1
Source/Guidelines/en/SG-GentleIntroduction.xml:11
Source/Specs/att.linguistic.xml:1
Source/Specs/att.lexicographic.normalized.xml:5