refresh: Make dependency on (guix import crates) weak.

Reported by Tobias Geerinckx-Rice <me@tobias.gr>.

* guix/scripts/refresh.scm: Do not explicitly import (guix import crates).

guix/scripts/refresh.scm

@@ -39,7 +39,6 @@
                           %kernel.org-updater))
   #:use-module (guix import elpa)
   #:use-module (guix import cran)
-  #:use-module (guix import crate)
   #:use-module (guix import hackage)
   #:use-module (guix gnupg)
   #:use-module (gnu packages)