nix: add postgrest-with-postgresql-17

PostgreSQL 17 has been released:
https://www.postgresql.org/about/news/postgresql-17-released-2936/

Let's make sure CI runs with it, too.

nix/overlays/default.nix

@@ -4,6 +4,5 @@
   gitignore = import ./gitignore.nix;
   haskell-packages = import ./haskell-packages.nix;
   postgresql-libpq = import ./postgresql-libpq.nix;
-  postgresql-future = import ./postgresql-future.nix;
   slocat = import ./slocat.nix;
 }