The. Builder installed temporary stairs of particle board. Should we remove these prior to installing the Permanent stairs and risers?
Purpose-built bullnose 1-1/4" particle board treads are a common and perfectly acceptable permanent tread solution. They've been the standard under carpeting in my region since at least the 1980s.
The only time they're a concern is when there's significant moisture contact, but then there are usually other problems of larger magnitude.
Now if you're asking because you're putting in full-thickness (1" or better) hardwood treads, then yes, you'd remove those.