Remove i18n comments from guitranslations

Nobody is looking at that file for context hints after ITS tool.
ITS tool: Extract `comment=` as comment for translators
ITS tool: Strip comments explaining the (itstool) paths

Our not-so-advanced layout engine doesn't require xml files where it
would be impossible to find location of the string matched. On the other
hand, comments like these ones were showing up in Weblate:
  #. (itstool) path: Container/Label@text
confusing translators for no gain whatsoever.
Maintenance work on create_pot