ruff

68ea2b8b - [red-knot] simplify "removing" in UnionBuilder::add (#16947)

[red-knot] simplify "removing" in UnionBuilder::add (#16947) ## Summary Simplify "removing" in UnionBuilder::add It's now O(m) instead of O(n + m) and easier to read. ## Test Plan cargo test (incl. mdtest)