Auto merge of #155671 - nnethercote:simplify-Config-track_state, r=bjorn3

Simplify `Config::track_state`.

This is a callback used to track otherwise untracked state. It was added in rust-lang/rust#116731 for Clippy. (It was originally named `hash_untracked_state`, and examples in the rustc-dev-guide still use that name.) The `StableHasher` argument is unused, and probably has never been used. There is a FIXME comment pointing this out, which was added more than a year ago.

This commit removes the `StableHasher` callback argument. This also removes the need for `Options::untracked_state_hash`.

r? @bjorn3

Author: bors