etc: Remove hydra.gnu.org.pub key.

* etc/substitutes/hydra.gnu.org.pub: Delete file.
* guix/self.scm (miscellaneous-files): Don't install it.
* Makefile.am (dist_pkgdata_DATA): Remove it.
* gnu/services/base.scm (%default-authorized-guix-keys): Likewise.
(hydra-key-authorization): Rename to…
(substitute-key-authorization): …this.  Adjust only call site.

Makefile.am

@@ -489,9 +489,8 @@ check-system: $(GOBJECTS)
 	   -e '(@@ (run-system-tests) run-system-tests)'	\
 	   $(top_srcdir)/build-aux/run-system-tests.scm
 
-# Public key used to sign substitutes from hydra.gnu.org & co.
+# Public keys used to sign substitutes.
 dist_pkgdata_DATA =				\
-  etc/substitutes/hydra.gnu.org.pub		\
   etc/substitutes/berlin.guixsd.org.pub		\
   etc/substitutes/ci.guix.gnu.org.pub		\
   etc/substitutes/ci.guix.info.pub

gnu/services/base.scm

@@ -1533,7 +1533,7 @@ GID."
     (('gnu rest ...) #t)
     (rest #f)))
 
-(define (hydra-key-authorization keys guix)
+(define (substitute-key-authorization keys guix)
   "Return a gexp with code to register KEYS, a list of files containing 'guix
 archive' public keys, with GUIX."
   (define default-acl
@@ -1570,8 +1570,7 @@ archive' public keys, with GUIX."
 
 (define %default-authorized-guix-keys
   ;; List of authorized substitute keys.
-  (list (file-append guix "/share/guix/hydra.gnu.org.pub")
-        (file-append guix "/share/guix/berlin.guixsd.org.pub")))
+  (list (file-append guix "/share/guix/berlin.guixsd.org.pub")))
 
 (define-record-type* <guix-configuration>
   guix-configuration make-guix-configuration
@@ -1688,7 +1687,7 @@ archive' public keys, with GUIX."
 
      ;; Optionally authorize substitute server keys.
      (if authorize-key?
-         (hydra-key-authorization keys guix)
+         (substitute-key-authorization keys guix)
          #~#f))))
 
 (define* (references-file item #:optional (name "references"))

gnu/system/install.scm

@@ -330,8 +330,8 @@ Access documentation at any time by pressing Alt-F2.\x1b[0m
           ;; The usual services.
           (syslog-service)
 
-          ;; The build daemon.  Register the hydra.gnu.org key as trusted.
-          ;; This allows the installation process to use substitutes by
+          ;; The build daemon.  Register the default substitute server key(s)
+          ;; as trusted to allow the installation process to use substitutes by
           ;; default.
           (service guix-service-type
                    (guix-configuration (authorize-key? #t)))

guix/self.scm

@@ -577,9 +577,6 @@ load path."
                    ,(file-append* source "/etc/completion/zsh/_guix"))
                   ("share/fish/vendor_completions.d/guix.fish"
                    ,(file-append* source "/etc/completion/fish/guix.fish"))
-                  ("share/guix/hydra.gnu.org.pub"
-                   ,(file-append* source
-                                  "/etc/substitutes/hydra.gnu.org.pub"))
                   ("share/guix/berlin.guixsd.org.pub"
                    ,(file-append* source
                                   "/etc/substitutes/berlin.guixsd.org.pub"))