gnu-maintenance: ‘gnu-ftp’ updater excludes GnuPG-hosted packages.

Since ftp://ftp.gnupg.org no longer exists, another updater should be
used for packages with code fetched from mirror://gnupg.

* guix/gnu-maintenance.scm (gnupg-hosted?): New procedure.
(%gnu-ftp-updater): Exclude packages that match ‘gnupg-hosted?’.
* guix/download.scm (%mirrors): Remove ftp://ftp.gnupg.org.

Change-Id: I653877ad843da60281d3a234acc85743bee64856

guix/download.scm

@@ -78,8 +78,7 @@ (define %mirrors
        "ftp://mirrors.dotsrc.org/gcrypt/"
        "ftp://ftp.heanet.ie/mirrors/ftp.gnupg.org/gcrypt/"
        "ftp://ftp.mirrorservice.org/sites/ftp.gnupg.org/gcrypt/"
-       "ftp://ftp.ring.gr.jp/pub/net/gnupg/"
-       "ftp://ftp.gnupg.org/gcrypt/")
+       "ftp://ftp.ring.gr.jp/pub/net/gnupg/")
       (gnome
        "https://download.gnome.org/"
        "http://ftp.gnome.org/pub/GNOME/")

guix/gnu-maintenance.scm

@@ -1025,15 +1025,19 @@ (define %gnu-updater
            (false-if-networking-error (gnu-hosted? package))))
    (import import-gnu-release)))
 
+(define gnupg-hosted?
+  (url-prefix-predicate "mirror://gnupg/"))
+
 (define %gnu-ftp-updater
   ;; This is for GNU packages taken from alternate locations, such as
-  ;; alpha.gnu.org, ftp.gnupg.org, etc.  It is obsolescent.
+  ;; alpha.gnu.org (ftp.gnupg.org is no longer available).  It is obsolescent.
   (upstream-updater
    (name 'gnu-ftp)
    (description "Updater for GNU packages only available via FTP")
    (pred (lambda (package)
            (false-if-networking-error
             (and (not (gnu-hosted? package))
+                 (not (gnupg-hosted? package))
                  (pure-gnu-package? package)))))
    (import import-release*)))