Those are fields used by the language switcher to correlate pages across
different languages, even if they have different names/paths/titles.
They are generated with the prepare_for_translation.py script.
This was never enforced (and the way it's written is not enforceable).
So, lets remove dead text.
If we'd like to enforce something like this in the future, we'd need to
require contributors signing CLA. But it wouldn't apply to past
contributions anyway.
