Remove infill_sparse_combine setting
Remove infill_sparse_combine setting

In discussion, we deemed infill_sparse_thickness more clear to the user and infill_sparse_combine superfluous, since it is really an intermediary value used by the engine to round the thickness up. So now it is actually computed in the engine. Accompanying this commit will be a commit to CuraEngine to remove the setting from the .json file.

fieldOfView/Cura,hmflash/Cura,bq/Ultimaker-Cura,totalretribution/Cura,Curahelper/Cura,totalretribution/Cura,ynotstartups/Wanhao,fieldOfView/Cura,senttech/Cura,markwal/Cura,ynotstartups/Wanhao,markwal/Cura,senttech/Cura,bq/Ultimaker-Cura,hmflash/Cura,Curahelper/Cura