Disable gzip compression in Caddyfile

Currently Akkoma doesn't have any proper mitigations against BREACH,
which exploits the use of HTTP compression to exfiltrate sensitive data.
(see: #721 (comment))

To err on the side of caution, disable gzip compression for now until we
can confirm that there's some sort of mitigation in place (whether that
would be Heal-The-Breach on the Caddy side or any Akkoma-side
mitigations).

installation/caddy/Caddyfile

@@ -12,8 +12,6 @@ example.tld  {
     output file /var/log/caddy/akkoma.log
   }
 
-  encode gzip
-
   # this is explicitly IPv4 since Pleroma.Web.Endpoint binds on IPv4 only
   # and `localhost.` resolves to [::0] on some systems: see issue #930
   reverse_proxy 127.0.0.1:4000