Do I need to?
Do I need to do surface preparation; won't the primer fix the bond problem? Or is there a primer that can go over the residues?
At face value these appear to be valid questions. However, there is a misconception that when the overlying applied material lets go, it is because it hasn't bonded to the residues, but a primer will stick it all together.
The reality is that the primer might help the applied adhesive/smoothing cement/membrane adhere to the residues, but that does not mean the residues will remain bonded to the substrate. ARDEX commonly see complaint materials with primer and residues on the bottom face!