Duh!  I'm so sorry about this.  I had check some days (weeks?) ago, saw
it wasn't there, prepared the package then rebased.  In the meantime
Sharlatan had committed it too!

Maybe we could have a `make` or `guix lint` warning for this kind of
things, I suppose they are bound to happen in the *-xyz files.

I'll revert my commit.

I'll be more careful about this pitfall next time, and thanks for
catching this!