Replace ($var sym) with ($values (sym)).

Replace ($var sym) with ($values (sym)).

* module/language/cps.scm: Remove $var.  Replaced by $values with one
  value.

* module/language/cps/arities.scm:
* module/language/cps/closure-conversion.scm:
* module/language/cps/compile-rtl.scm:
* module/language/cps/dfg.scm:
* module/language/cps/slot-allocation.scm:
* module/language/cps/verify.scm:
* module/language/tree-il/compile-cps.scm: Adapt all the world.