First, Wikipedia says nothing of the sort that I can see. Type in "Don Quixote" and go to "pronunciation" and it supports my pronunciation.

However, if there is another site or page that says the x had changed to /h/, that site or page is wrong. How do we know this? Simple. The rendering of Aztec words made by Carochi and other Spaniards used x for /sh/.

More to the point, Carochi, in his Grammar of Nahuatl of 1645, feels the need to explain a few sounds - for example, "usan del o algunas vezes tan cerrada, y obscura, que tira algo à la pronunciacion de la u". However, he felt no need to clarify that the x is /sh/, as at the time of printing (1645) it was a current pronunciation. That he should have realized he needed to say something if it had been different can be seen in his note "Tampoco se pronuncia la n antes de la x sino que la x se pronuncia con mas fuerça".