This is for completions in "M-x guix r =t".

In 'emacs/guix-main.scm' I used:

  (map (@ (guix upstream) upstream-updater-name)
       (@ (guix scripts refresh) %updaters)))

instead of adding these modules to the top-level (use-modules ...) to
avoid loading them on start.  If it's OK, I'm going to do the same for
(guix scripts graph) and (guix scripts lint) modules, as they are used
only to get graph types and lint checkers.