Should I withdraw my other PhD applications when I have a secured funding and a supervisor but I am waiting for the faculty decision?
No!

Until you receive an official offer of admission, you have not been accepted to the PhD program. Do not withdraw your other applications until you have actually been accepted somewhere.

(In fact, I would not recomend withdrawing your applications at all, but rather, if possible, waiting until you have all your official admissions offers and then deciding which one to accept.)