Check for struct shape removal in Pancake's Return semantics

Multivalued return is now implemented so the check in Pancake semantics for struct fitting inside the `Temp` stores at wordLang is unnecessary and can be removed from here.
```
(evaluate (Return e,s) =
case (eval s e) of
| SOME value =>
if size_of_sh_with_ctxt s.structs (shape_of value) <= 32
then (SOME (Return value),empty_locals s)
else (SOME Error,s)
| _ => (SOME Error,s)) /\
```

Start by locating Pancake's Return semantics and the wordLang Temp-store check shown in the issue. Confirm how multivalued returns are handled, remove the struct-shape size check, and verify that the existing Pancake semantics checks still pass without the obsolete condition.

Written by the indexing model from the issue text.