Reduce stair step height to 0 for PVA
Given that:
* stair stepping is intended to be used to reduce the adhesion between support and the model, where the support rests on the model, and to reduce scarring, and
* PVA doesn't suffer from scarring or adhesion issues due to its water-solubility, and
* our current stair stepping algorithm has some bugs, causing support to disappear sometimes
we've decided to set stair stepping to 0 for all PVA profiles for UM3, UMS5 and UMS3.
Contributes to issue CURA-7311.