[2027-01-01] Remove library xml redirect/mechanism

Because kiwix-android uses (to this day) URL https://mirror.download.kiwix.org/library/library_zim.xml to fetch the library, we have added a redirect in the master mirror to point it to an up-to-date version.
We want this gone as soon as possible.
To be considered on 2027

- https://github.com/kiwix/kiwix-android/issues/4861
- https://github.com/kiwix/operations/issues/608

Start by reviewing kiwix-android issue #4861 and operations issue #608 to identify the redirect and confirm whether the old library URL is still used. Trace the redirect in the operations infrastructure, then verify the mechanism is removed only after the linked consumer no longer depends on it.

Written by the indexing model from the issue text.