build: Default to https://ci.guix.info for substitutes.

* config-daemon.ac (guix_substitute_urls): Always default to
"https://ci.guix.info".
* doc/guix.texi (SUBSTITUTE-SERVER): Switch to ci.guix.info.
* guix/scripts/build.scm (%default-log-urls): Likewise.
* guix/scripts/substitute.scm (%default-substitute-urls): Likewise.
* guix/store.scm (%default-substitute-urls): Likewise.

config-daemon.ac

@@ -120,15 +120,7 @@ if test "x$guix_build_daemon" = "xyes"; then
 
   dnl Determine the appropriate default list of substitute URLs (GnuTLS
   dnl is required so we can default to 'https'.)
-  case "x$host_cpu" in
-    xaarch64)
-      # Currently only berlin.guixsd.org provides aarch64 binaries.
-      guix_substitute_urls="https://berlin.guixsd.org"
-      ;;
-    *)
-      guix_substitute_urls="https://mirror.hydra.gnu.org"
-      ;;
-  esac
+  guix_substitute_urls="https://ci.guix.info"
 
   AC_MSG_CHECKING([for default substitute URLs])
   AC_MSG_RESULT([$guix_substitute_urls])

doc/guix.texi

@@ -14,7 +14,7 @@
 @set KEY-SERVER pool.sks-keyservers.net
 
 @c The official substitute server used by default.
-@set SUBSTITUTE-SERVER ci.guix.info
+@set SUBSTITUTE-SERVER mirror.hydra.gnu.org
 
 @copying
 Copyright @copyright{} 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès@*
@@ -2374,14 +2374,9 @@ Then, you can run something like this:
 @end example
 
 @quotation Note
-Similarly, the @file{berlin.guixsd.org.pub} file contains the public key
-for the project's new build farm, reachable at
-@indicateurl{https://berlin.guixsd.org}.
-
-As of this writing @code{berlin.guixsd.org} is being upgraded so it can
-better scale up, but you might want to give it a try.  It is backed by
-20 x86_64/i686 build nodes and may be able to provide substitutes more
-quickly than @code{mirror.hydra.gnu.org}.
+Similarly, the @file{hydra.gnu.org.pub} file contains the public key
+of an independent build farm also run by the project, reachable at
+@indicateurl{https://mirror.hydra.gnu.org}.
 @end quotation
 
 Once this is in place, the output of a command like @code{guix build}

guix/scripts/build.scm

@@ -65,7 +65,7 @@
 
 (define %default-log-urls
   ;; Default base URLs for build logs.
-  '("http://hydra.gnu.org/log"))
+  '("http://ci.guix.info/log"))
 
 ;; XXX: The following procedure cannot be in (guix store) because of the
 ;; dependency on (guix derivations).

guix/scripts/substitute.scm

@@ -1052,7 +1052,7 @@ found."
     (#f
      ;; This can only happen when this script is not invoked by the
      ;; daemon.
-     '("http://hydra.gnu.org"))))
+     '("http://ci.guix.info"))))
 
 (define substitute-urls
   ;; List of substitute URLs.

guix/store.scm

@@ -693,7 +693,7 @@ encoding conversion errors."
   (map (if (false-if-exception (resolve-interface '(gnutls)))
            (cut string-append "https://" <>)
            (cut string-append "http://" <>))
-       '("mirror.hydra.gnu.org")))
+       '("ci.guix.info")))
 
 (define* (set-build-options server
                             #:key keep-failed? keep-going? fallback?