[ocsigen-start.8.0.0] Constrain ocsigen-i18n < 5.0.0

ocsigen-i18n 5.0.0 generates [@@deriving json] directly in --eliom
mode. ocsigen-start 8.0.0 has a sed post-processing step that also
adds [@@deriving json], causing duplication and a compilation error.
Add an upper bound to prevent the incompatible combination.

Also remove the duplicate ocsigen-i18n dependency entry.

Author: balat

packages/ocsigen-start/ocsigen-start.8.0.0/opam

@@ -20,11 +20,10 @@ depends: [
   "pgocaml" {>= "4.0"}
   "pgocaml_ppx" {>= "4.0"}
   "safepass" {>= "3.0"}
-  "ocsigen-i18n" {>= "4.0.0"}
+  "ocsigen-i18n" {>= "4.0.0" & < "5.0.0"}
   "eliom" {>= "12.0.0" & < "13.0.0"}
   "ocsigen-toolkit" {>= "2.7.0"}
   "ocsigen-ppx-rpc" {>= "1.1"}
-  "ocsigen-i18n" {>= "3.7.0"}
   "yojson" {>= "1.6.0"}
   "resource-pooling" {>= "1.0" & < "2.0"}
   "cohttp-lwt-unix"