Cleanup after removal of labels (Pancake)

[mktnk3]

The labels are now removed from the Pancake syntax, but there are still some residual syntactic redundancy that we should clean up. Namely,

Datatype:
  word_lab = Word ('a word)
  (* labels were defined here *)
End

Datatype:
  v = Val ('a word_lab)
    | Struct (v list)
End

Overload ValWord  = “\w. Val (Word w)”

should be just:

Datatype:
  v = Val ('a word)
    | Struct (v list)
End