Set PostgreSQL package to PostgreSQL 15 for netbox host

Also remove the upgrade script again.

Bascially do steps 4 and 5 of the following section of the manual:
https://nixos.org/manual/nixos/stable/#module-services-postgres-upgrading

config/hosts/netbox/postgresql.nix

@@ -1,33 +1,7 @@
 { pkgs, config, ... }:
 
 {
-  # Modified version of the script for upgrading PostgreSQL from here:
+  services.postgresql = {
-  # https://nixos.org/manual/nixos/stable/#module-services-postgres-upgrading
+    package = pkgs.postgresql_15;
-  environment.systemPackages = [
+  };
-    (let
-      newPostgres = pkgs.postgresql_15;
-    in pkgs.writeScriptBin "upgrade-pg-cluster" ''
-      set -eux
-
-      systemctl stop netbox.service netbox-rq.service
-      systemctl stop redis-netbox.service
-      systemctl stop postgresql.service
-
-      export NEWDATA="/var/lib/postgresql/${newPostgres.psqlSchema}"
-
-      export NEWBIN="${newPostgres}/bin"
-
-      export OLDDATA="${config.services.postgresql.dataDir}"
-      export OLDBIN="${config.services.postgresql.package}/bin"
-
-      install -d -m 0700 -o postgres -g postgres "$NEWDATA"
-      cd "$NEWDATA"
-      sudo -u postgres $NEWBIN/initdb -D "$NEWDATA"
-
-      sudo -u postgres $NEWBIN/pg_upgrade \
-        --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
-        --old-bindir $OLDBIN --new-bindir $NEWBIN \
-        "$@"
-    '')
-  ];
 }