Firstly lets make the assumption that this team is indeed running Landorus, since standard VoltTurn only requires Scizor and Wash, with Landorus being more likely to be present if on a Sand team.
Once more, Celebi can switch into and beat Rotom-W everytime without fail. In order for Rotom-W to not become fodder it must Volt Switch every time, presumably to Landorus. Landorus forces Celebi out, but cannot do anything to, for example, Skarmory, which requires Landorus to consistently U-Turn, else it becomes set up fodder for Skarmory.
The player with Celebi clearly has two Pokemon that will repeatedly beat the ScizorWash supported by Landorus combo, hence, switches can be repeatedly made at no risk to the player. Now, if I am a halfway competent player, I will not spend 16 consecutive turns using either Volt Switch or U-Turn. At some point, the opposing player will overpredict, switch to a different Pokemon, etc. Ergo, Celebi, beating Scizor and Rot-W, combined with Skarmory, which beats the occasional associate Landorus, defeat VoltTurn.
Frankly I don't understand why the assumption is being made that Landorus always accompanies Scizor and Rotom-W when that is far from the case but for the purposes of the argument, you added one Pokemon that beats Celebi, I countered by adding a second standard Pokemon that beats Landorus making the initial point remain valid.
I won't continue further on this topic since I've stated and restated my arguments several times against repetitive attempts to undermine my claim.
Have a nice day, and happy ScizorWash destroying for those inspired to use Celebi.
EDIT: Actually, one final point.
Hardly an obvious move choice given that in that same slot, both Earth Power and Psychic are also slashed, not to mention that HP Fire, along with Thunder Wave, are the most likely slots to be replaced with an AC/OO move option. The sheer fact that the two main options are walled by Heatran and that a coverage move against Heatran is slashed makes it utterly foolish to naively expect HP Fire on Tinkerbell.