Ensure we remove ProcessLayersJob once it has finished
Ensure we remove ProcessLayersJob once it has finished

Since it holds on to a fairly large amount of data.

Contributes to CURA-2406

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