Port `examples`, `interactions`, etc., to use the new `examples` form of `scribble/examples`. The main intended effect is to ensure that errors are produced by examples only as specifically indicated.
The development history for set-of-scopes is preserved in a "scope" branch in the main Racket repository, which is commit ae88c96f50
ae88c96f50
The layer is now redundant, since everything left in "pkgs" is in the "racket-pkgs" category.