Further simplifications in type checker.
Further simplifications in type checker.

HIPERFIT/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,diku-dk/futhark,ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark