Drop `rescue TSort::Cyclic` from `Gem::{DependencyList,RequestSet}#tsort_each_child`.

`TSort::Cyclic` is only raised from `TSort.tsort_each`, not from `TSort#strongly_connected_components` which is used here. Even then, the exception is raised outside the child iterator and thus cannot be rescued in `#tsort_each_child`.

This is only a cosmetic change that doesn't affect compatibility.

Originally introduced in f554bc5 and a1d35cd, respectively.