whats the pros and cons of removing this stepping motor and controlling the boost entirely with a manual boost controller.

 

a friend of mine did this in his Z ...

If I see it correctly that is the low / high boost solenoid. If you have a boost controller you won't need it. It controls the boost and lowers it in times of trouble. Without it you can risk your motor as some of the safety features will be removed. All depends on what mods you've done and how safe they are.

you can remove the wastgate solenoids, but you will need an electronic boost controller. Not a real problem, however pointless, as when you fit a electronic controller you disconect the solenoids anyway, and just bypassing, so leave them there, unless you wish to save 2lb in weight.