It *was* the trinket you received in the process of completing the Swift Flight Form questline. It was called the
"Charm of Swift Flight" ..sadly last patch or so, it was changed. Now it reduces the mana cost of flight form. It was changed for the same reason riding crops no longer work after level 70. In a effort to make enchantments, instead of trinkets. Blizzard encounter some issue with this process, which is now on hold.