Rollup merge of #120866 - Zalathar:no-min-spec, r=compiler-errors

Remove unnecessary `#![feature(min_specialization)]`

As of #119963 and #120676, we can now rely on `newtype_index!` having `#[allow_internal_unstable(min_specialization)]`, so there are a few compiler crates that no longer need to include min-spec in their own crate features.

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Some of the expansions of `newtype_index!` still appear to require min-spec in the crate features. I think this is because `#[orderable]` causes the expansion to include an implementation of `TrustedStep`, which is flagged with `#[rustc_specialization_trait]`, and for whatever reason that isn't permitted by allow-internal-unstable. So this PR only touches the crates where that isn't the case.