Fix worker/wrapper ids for newtype instances
- mkDataConIds forced an algebraic worker/wrapper on newtype instances (not on vanilla newtypes). I am not sure where this came from (from code I wrote or from the recent restructuring of MkIds), but its not the right thing to do. In particular, it requires newtype instances to have con_info labels in the generated code, which makes no sense. - Worker construction for newtypes is smart enough that it will construct the right signature for newtype instances (ie, one that mentions the family type constructor, not the instance tycon).