build: Substitute URLs now default to "mirror.hydra.gnu.org" alone.

* config-daemon.ac: Remove "hydra.gnu.org" from 'guix_substitute_urls'.
* guix/store.scm (%default-substitute-urls): Remove "hydra.gnu.org".

config-daemon.ac

@@ -113,10 +113,10 @@ if test "x$guix_build_daemon" = "xyes"; then
   dnl Determine the appropriate default list of substitute URLs.
   GUILE_MODULE_AVAILABLE([have_gnutls], [(gnutls)])
   if test "x$have_gnutls" = "xyes"; then
-    guix_substitute_urls="https://mirror.hydra.gnu.org https://hydra.gnu.org"
+    guix_substitute_urls="https://mirror.hydra.gnu.org"
   else
     AC_MSG_WARN([GnuTLS is missing, substitutes will be downloaded in the clear])
-    guix_substitute_urls="http://mirror.hydra.gnu.org http://hydra.gnu.org"
+    guix_substitute_urls="http://mirror.hydra.gnu.org"
   fi
   AC_MSG_CHECKING([for default substitute URLs])
   AC_MSG_RESULT([$guix_substitute_urls])

guix/store.scm

@@ -510,7 +510,7 @@ (define %default-substitute-urls
   (map (if (false-if-exception (resolve-interface '(gnutls)))
            (cut string-append "https://" <>)
            (cut string-append "http://" <>))
-       '("mirror.hydra.gnu.org" "hydra.gnu.org")))
+       '("mirror.hydra.gnu.org")))
 
 (define* (set-build-options server
                             #:key keep-failed? keep-going? fallback?