gnu: openssh: Clean-up custom install phase.

* gnu/packages/ssh.scm (openssh)[arguments]: Factor out outputs in
custom 'install phase to clean-up code.

gnu/packages/ssh.scm

@@ -220,20 +220,17 @@ a server that supports the SSH-2 protocol.")
            #t))
         (replace 'install
          (lambda* (#:key outputs (make-flags '()) #:allow-other-keys)
-           ;; install without host keys and system configuration files
-           (apply invoke "make" "install-nosysconf" make-flags)
-           (install-file "contrib/ssh-copy-id"
-                         (string-append (assoc-ref outputs "out")
-                                        "/bin/"))
-           (chmod (string-append (assoc-ref outputs "out")
-                                 "/bin/ssh-copy-id") #o555)
-           (install-file "contrib/ssh-copy-id.1"
-                         (string-append (assoc-ref outputs "out")
-                                        "/share/man/man1/"))
-           ;; Don't install the PRIVSEP_PATH directory.
-           (delete-file-recursively
-             (string-append (assoc-ref outputs "out") "/var"))
-           #t)))))
+           (let ((out (assoc-ref outputs "out")))
+             ;; install without host keys and system configuration files
+             (apply invoke "make" "install-nosysconf" make-flags)
+             (install-file "contrib/ssh-copy-id"
+                           (string-append out "/bin/"))
+             (chmod (string-append out "/bin/ssh-copy-id") #o555)
+             (install-file "contrib/ssh-copy-id.1"
+                           (string-append out "/share/man/man1/"))
+             ;; Don't install the PRIVSEP_PATH directory.
+             (delete-file-recursively (string-append out "/var"))
+             #t))))))
    (synopsis "Client and server for the secure shell (ssh) protocol")
    (description
     "The SSH2 protocol implemented in OpenSSH is standardised by the