WoWDB

Awarded to players who completed the now unused attunement quests to Black Temple and The Battle for Mount Hyjal Prior too patch 3.0 (Wrath pre patch) and is currently unobtainable for new players. Players with this FoS on any characters will unlock the title "[Name], Hand of A'dal" on all lvl 70 or over characters tied to that Battle.net account. 

Note if you have any Alts who started and completed some of the attunement quests prior to 3.0 and still have them in their quest logs, this achievement is still available on that toon, This was confirmed as still working as of 4.3 by a guild member, Unsure if it works after 5.0

Still works in Mists of Pandaria.

Didn't they wipe obsolete quests from our log, though, in Cataclysm?

Technically, I don't think the quest is flagged as obsolete; it just isn't available for newer players to acquire.  Contrast The Vials of Eternity with The Perfect Poison.  Anyway, according to Wowhead comments, it's still possible.  Some have posted proof, too - Ayrila @ EU-Executus.