Auto merge of #5528 - phansch:same-tys, r=flip1995

Cleanup: Use rustc's `same_type` for our `same_tys`

This delegates our `same_tys` to [ty::TyS::same_type][same_type] to
remove some duplication.

Our `same_tys` was introduced 4 years ago in #730. Before, it was
building an inference context to be able to call
`can_eq` to compare the types. The `rustc-dev-guide` has some more details
about `can_eq` in [Type Inference -> Trying equality][try_eq].

Now, using the rustc function, we are essentially comparing the `DefId`s
of the given types, which also makes more sense, IMO.

I also confirmed that the FIXME is resolved via a bit of `dbg!`, however
no UI tests seem to have been affected.

[same_type]: https://github.com/rust-lang/rust/blob/659951c4a0d7450e43f61c61c0e87d0ceae17087/src/librustc_middle/ty/util.rs#L777
[try_eq]: https://rustc-dev-guide.rust-lang.org/type-inference.html#trying-equality

---

changelog: none

0 files changed, 0 insertions, 0 deletions