Adjust references to terms defined in the Permissions spec.

[rakuco]

• Use [=powerful feature/name=] dfn instead of a custom one, as it is now Bikeshed's spec-data.
• Similarly, [=permission status=] is also defined in spec-data, so reference it from there (this also fixes the reference, which was pointing to an invalid anchor in the Permissions spec).

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[anssiko]

Thanks again!