Rely on upstream package to supply typing and challenge-bypass-ristretto as
necessary.  Simplify our expression (approximately pointfree style) so we
don't have to know about any other arguments that might be passed or accepted.

At least, I suppose it was incorrect.  It won't build anywhere it has not
already built.  I don't know how it built where it already built.

why make it a plugin, then, you may ask.
or perhaps you may not ask.

overrides

They're not necessary on newly selected nixpkgs revision.

The layer above will have to make sure that it is.

This gives us the merged version of Ristretto support.