[BUGFIX] Streamline language pack download URLs

* t3o has fileadmin/l10n since 2 years (currently it's a redirect).
* new translation server just took the path as previously on t3o

This is now consolidated:
* t3o is replacing fileadmin/ter with fileadmin/l10n (saving t3o some redirects)
* localize is using xliff/

Both changes are in place already on the remote servers so this change
can be used directly.

Resolves: #84025
Releases: master, 9.5
Change-Id: I6362f6f0f8dbc6739f007deb82edb54de608d21c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63533


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>