Use the new matching() for latin.c.

The new client code is a lot smaller and nicer, because we can throw
away the col[] and num[] permutations entirely.

Of course, this also means that every puzzle that incorporated latin.c
now has to link against matching.c instead of maxflow.c - but since I
centralised that secondary dependency into Recipe a few commits ago,
it's trivial to switch them all over at once.