remove redundant .gitlab-ci.dhall

.gitlab-ci.dhall

-let Prelude =
-        env:DHALL_PRELUDE
-      ? https://raw.githubusercontent.com/dhall-lang/dhall-lang/v20.1.0/Prelude/package.dhall
-          sha256:26b0ef498663d269e4dc6a82b0ee289ec565d683ef4c00d0ebdd25333a5a3c98
-
-let H = ./horizon-spec.dhall
-
-let Step = { script : List Text }
-
-let toStep
-    : ∀(id : Text) → ∀(prefix : Text) → ∀(x : Text) → H.Attr Step
-    = λ(id : Text) →
-      λ(prefix : Text) →
-      λ(x : Text) →
-        { mapKey = id, mapValue.script = [ "nix build -L .#${prefix}.${x}" ] }
-
-let input = Prelude.Map.keys Text H.HaskellPackage.Type (./horizon.dhall).packages
-
-let packages =
-      Prelude.List.map
-        Text
-        (H.Attr Step)
-        (λ(x : Text) → toStep "Package ${x}" "packages.x86_64-linux" x)
-        (input : List Text)
-
-in  packages