Update src/passes/DeadArgumentElimination.cpp

Co-authored-by: Thomas Lively <tlively123@gmail.com>

Author: kripken

src/passes/DeadArgumentElimination.cpp

@@ -618,7 +618,7 @@ struct DAE : public Pass {
       builder[0].subTypeOf(func->type);
       // Make this subtype open like the super. This is not necessary, but might
       // allow more work later after other changes, in theory.
-      builder.setOpen(0, true);
+      builder[0].setOpen();
       auto result = builder.build();
       assert(!result.getError());
       func->type = (*result)[0];