By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Review cleanups: drop unused Validity/RankNTypes, fix stale doc - Remove the unused 'instance Validity NoExtField'. - Remove the now-unused RankNTypes pragma from the aeson interpreters (the handler records are no longer rank-2). - Fix the stale 'ToJSONExt' haddock (extension nodes are no longer context-polymorphic) and document that the caller-supplied encode/decode handlers must be kept mutually consistent.