services: openssh: Install OpenSSH in the system profile.

This ensures one can scp to or from the GuixSD machine that uses the
service.

* gnu/services/ssh.scm (openssh-service-type)[extensions]: Add
PROFILE-SERVICE-TYPE extension.
* gnu/system/examples/bare-bones.tmpl <packages>: Remove OPENSSH.
* doc/guix.texi (Using the Configuration System): Adjust accordingly.

doc/guix.texi

@@ -9727,9 +9727,9 @@ environment variable---in addition to the per-user profiles
 provides all the tools one would expect for basic user and administrator
 tasks---including the GNU Core Utilities, the GNU Networking Utilities,
 the GNU Zile lightweight text editor, @command{find}, @command{grep},
-etc.  The example above adds GNU@tie{}Screen and OpenSSH to those,
-taken from the @code{(gnu packages screen)} and @code{(gnu packages ssh)}
-modules (@pxref{Package Modules}).  The
+etc.  The example above adds GNU@tie{}Screen to those,
+taken from the @code{(gnu packages screen)}
+module (@pxref{Package Modules}).  The
 @code{(list package output)} syntax can be used to add a specific output
 of a package:
 

gnu/services/ssh.scm

@@ -518,7 +518,15 @@ (define openssh-service-type
                        (service-extension activation-service-type
                                           openssh-activation)
                        (service-extension account-service-type
-                                          (const %openssh-accounts))))
+                                          (const %openssh-accounts))
+
+                       ;; Install OpenSSH in the system profile.  That way,
+                       ;; 'scp' is found when someone tries to copy to or from
+                       ;; this machine.
+                       (service-extension profile-service-type
+                                          (lambda (config)
+                                            (list (openssh-configuration-openssh
+                                                   config))))))
                 (compose concatenate)
                 (extend extend-openssh-authorized-keys)
                 (default-value (openssh-configuration))))

gnu/system/examples/bare-bones.tmpl

@@ -3,7 +3,7 @@
 
 (use-modules (gnu))
 (use-service-modules networking ssh)
-(use-package-modules screen ssh)
+(use-package-modules screen)
 
 (operating-system
   (host-name "komputilo")
@@ -40,7 +40,7 @@
                %base-user-accounts))
 
   ;; Globally-installed packages.
-  (packages (cons* screen openssh %base-packages))
+  (packages (cons screen %base-packages))
 
   ;; Add services to the baseline: a DHCP client and
   ;; an SSH server.