ci: Add missing imports.

This is a followup to 041a9466.

* guix/ci.scm: Add missing imports.
* guix/channels.scm: Remove (guix ci) import.

guix/channels.scm

@@ -20,7 +20,6 @@
 
 (define-module (guix channels)
   #:use-module (git)
-  #:use-module (guix ci)
   #:use-module (guix git)
   #:use-module (guix git-authenticate)
   #:use-module ((guix openpgp)

guix/ci.scm

 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2020 Mathieu Othacehe <othacehe@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -23,6 +23,8 @@ (define-module (guix ci)
   #:use-module (json)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
+  #:use-module (guix i18n)
+  #:use-module (guix diagnostics)
   #:autoload   (guix channels) (channel)
   #:export (build-product?
             build-product-id