Don't remove auxiliary text if mw is too old

If MediaWiki is too old a version to return filtered text then don't filter
auxiliary text from the page text because we have no way to get it back.
Instead just leave it in the page text and set auxiliary_text to an empty
array.

Bug: 71233
Change-Id: Icd15622cb7a112af59d60ecaaa91e62edb2dd19b
Merge "Don't remove auxiliary text if mw is too old"