channels: Turn off deprecation warnings when loading 'build-self.scm'.

* guix/channels.scm (build-from-source): Parameterize
DEPRECATION-WARNING-PORT when loading SCRIPT.

guix/channels.scm

@@ -27,6 +27,7 @@
   #:use-module (guix profiles)
   #:use-module (guix derivations)
   #:use-module (guix combinators)
+  #:use-module (guix deprecation)
   #:use-module (guix store)
   #:use-module (guix i18n)
   #:use-module ((guix utils)
@@ -275,7 +276,12 @@ package modules under SOURCE using CORE, an instance of Guix."
   (if (file-exists? script)
       (let ((build (save-module-excursion
                     (lambda ()
-                      (primitive-load script)))))
+                      ;; Disable deprecation warnings; it's OK for SCRIPT to
+                      ;; use deprecated APIs and the user doesn't have to know
+                      ;; about it.
+                      (parameterize ((deprecation-warning-port
+                                      (%make-void-port "w")))
+                        (primitive-load script))))))
         ;; BUILD must be a monadic procedure of at least one argument: the
         ;; source tree.
         ;;