Forbid xml:id on remark

[ghost]

Not quite sure if that is really possible but it would be great if we could just forbid xml:id attrs on <remark/> tags in GeekoDoc. I will (in shah Cthulhu) also add some code to the style checker regarding this -- if this can be fixed in GeekoDoc, I can do that just for elements nested within remark, otherwise I'd do it for both remark and elements nested within.