nixosTests.agda: Adapt to --guardedness requirements

The one-line test is hard to fix in a readable manner
and doesn't really add value above the hello-world test.
So rather simplify to reduce maintenance.

Changed files
+1 -4
nixos
tests
+1 -4
nixos/tests/agda.nix
···
let
hello-world = pkgs.writeText "hello-world" ''
+
{-# OPTIONS --guardedness #-}
open import IO
open import Level
···
# Minimal script that typechecks
machine.succeed("touch TestEmpty.agda")
machine.succeed("agda TestEmpty.agda")
-
-
# Minimal script that actually uses the standard library
-
machine.succeed('echo "import IO" > TestIO.agda')
-
machine.succeed("agda -l standard-library -i . TestIO.agda")
# Hello world
machine.succeed(