Remove old Windows CE cruft.

The WinCE version of these puzzles hasn't been built for years, and
the last vestiges of its build system vanished with the migration to
CMake. So this seems like a good moment to lose the rest of it.

So the supporting Perl script wceinf.pl is deleted, and so is all the
unused code under '#ifdef _WIN32_WCE' in windows.c. (I removed that
using unifdef, which did a more reliable job than I would have done by
hand!)