refine: remove dead commented-out code in window transform resolver

[prql-bot]

Found during the nightly code-quality survey of semantic/resolver/transforms.rs.

The window transform arm carried two commented-out lines that are superseded by the Range { start, end } construction immediately below them:

// let start = Expr::new(start.map_or(Literal::Null, Literal::Integer));
// let end = Expr::new(end.map_or(Literal::Null, Literal::Integer));
let range = Range {
    start: start.map(Literal::Integer).map(Expr::new).map(Box::new),
    end: end.map(Literal::Integer).map(Expr::new).map(Box::new),
};

Besides being dead, the commented-out version is now actively misleading: it maps None to Literal::Null via map_or, whereas the live code maps None to None (an absent bound) via map. A future reader comparing the two could reasonably think Null was the intended behavior. Removing the stale comment.

No behavioral change — the lines were never compiled. No regression test is applicable since nothing executable changed; verified with cargo build -p prqlc and the existing sql::gen_query::test::test_filter_windowed window test, both green.