nixos/lemmy: inline localPostgres into database assertion

Co-authored-by: Shahar Dawn Or <mightyiampresence@gmail.com>
Co-authored-by: Ctem <c@ctem.me>
Co-authored-by: a-kenji <aks.kenji@protonmail.com>
Co-authored-by: Brian Leung <leungbk@posteo.net>
Co-authored-by: Ilan Joselevich <personal@ilanjoselevich.com>

nixos/modules/services/web-apps/lemmy.nix

@@ -71,9 +71,6 @@ in
   };
 
   config =
-    let
-      localPostgres = (cfg.settings.database.host == "localhost" || cfg.settings.database.host == "/run/postgresql");
-    in
     lib.mkIf cfg.enable {
       services.lemmy.settings = (mapAttrs (name: mkDefault)
         {
@@ -100,7 +97,7 @@ in
         };
       });
 
-      services.postgresql = mkIf localPostgres {
+      services.postgresql = mkIf cfg.database.createLocally {
         enable = mkDefault true;
       };
 
@@ -141,7 +138,7 @@ in
       };
 
       assertions = [{
-        assertion = cfg.database.createLocally -> localPostgres;
+        assertion = cfg.database.createLocally -> cfg.settings.database.host == "localhost" || cfg.settings.database.host == "/run/postgresql";
         message = "if you want to create the database locally, you need to use a local database";
       }];