Remove iterability from ExtruderManager
Remove iterability from ExtruderManager

This is no longer used.

Contributes to issues CURA-1278 and CURA-340.

fieldOfView/Cura,totalretribution/Cura,ynotstartups/Wanhao,senttech/Cura,hmflash/Cura,senttech/Cura,Curahelper/Cura,hmflash/Cura,fieldOfView/Cura,totalretribution/Cura,Curahelper/Cura,ynotstartups/Wanhao