Remove last vestiges of assertZip checking from fusion.
Remove last vestiges of assertZip checking from fusion.

CulpaBS/wbBach,HIPERFIT/futhark,mrakgr/futhark,ihc/futhark,HIPERFIT/futhark,mrakgr/futhark,ihc/futhark,diku-dk/futhark,mrakgr/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark