backups: Simplify SSH fingerprint verification command

There is no need to access the private key of an SSH host to get it's public key
fingerprint. Use public key file instead. No need for 'sudo' privileges because
of this any non-admin users can also do this verification.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Joseph Nuthalapati <njoseph@riseup.net>

plinth/modules/backups/templates/verify_ssh_hostkey.html

@@ -65,7 +65,7 @@
             {% endblocktrans %}
           </p>
           <p>
-            <code>sudo ssh-keygen -lf /etc/ssh/ssh_host_rsa_key</code>
+            <code>ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub</code>
           </p>
         </div>
       </section>