two smaller feature cleanups

[cyrgani]

Remove an unneeded feature gate for a private macro and sort the used features correctly by whether they are language or library features.

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[cyrgani]

Maybe it would be better to remove the separation between lang and libs features at that point and merge them into a single big // tidy-alphabetical-start section?

[bjorn3]

According to #87766 the split between language and library features is for the following reason:

For the language features, we should check with the relevant team(s) if it's okay that we're using the feature in the library, and document with which of them we need to be extra careful and what their pitfalls are.