transpiler: `BuiltInCall` variant does not have field `return_type`

[Prestgg1]

Error

error[E0026]: variant `BuiltInCall` does not have a field named `return_type`
  --> crates/transpiler/src/helper.rs:53:13
   |
53 |             return_type,
   |             ^^^^^^^^^^^ variant `BuiltInCall` does not have this field

error[E0026]: variant `BuiltInCall` does not have a field named `return_type`
  --> crates/transpiler/src/lib.rs:38:13
   |
38 |             return_type,
   |             ^^^^^^^^^^^ variant `BuiltInCall` does not have this field

The Expr::BuiltInCall variant doesn't have a return_type field. The transpiler pattern match tries to destructure it, but it doesn't exist.

[Prestgg1]

Superseded by #16 which covers all transpiler compilation errors after API changes.