Delete some of my commented-out prototype code.

Delete some of my commented-out prototype code.

The new Tui structure now replicates almost all the useful
functionality of that. The only exception is the extra loop where we
re-split each line returned from render() to the screen width, in case
it's overlong. But that can't be centralised into the current code: it
will have to live in the draw() method of ActivityState types that
need it (particularly, those rendering paragraphs), because they'll
need to know when it happened in order to count screen lines
correctly.