remove some stuff from xmldiff example

[yomimono]

module Op looks like a vestigial thing that can be removed since the definition of gens in crowbar.mli now matches it; can you confirm or deny, @stedolan ?

I also removed what looked like some inessential weirdness in defining ident and elem_name, but let me know if I'm misunderstanding something subtle.

[stedolan]

inessential weirdness

this is my new band name

[yomimono]

be sure to cite https://www.crummy.com/sumana/2016/05/21/0 and http://www.classmatters.org/2006_07/its-not-them.php at all your shows 🎸