Enable ed25519 collator in voting.

Previously, I had left in some debugging code with /*XXX*/ after it,
which nobody noticed.  Live and learn!  Next time I will use /*XXX
DO NOT COMMIT*/ or something.

We need to define a new consensus method for this; consensus method
21 shouldn't actually be used.

Fixes bug 17702; bugfix on 0.2.7.2-alpha.