ci: simplify test

Remove obsolete features that were required for pkgsUnstable.

test/ci/build.sh

@@ -7,9 +7,7 @@
 
 set -euo pipefail
 
-scenario=${scenario:-}
-
-if [[ -v CIRRUS_CI && $scenario ]]; then
+if [[ -v CIRRUS_CI ]]; then
     if [[ ! -e /dev/kvm ]]; then
         >&2 echo "No KVM available on VM host."
         exit 1
@@ -20,10 +18,4 @@ fi
 
 echo "$NIX_PATH ($(nix eval --raw nixpkgs.lib.version))"
 
-if [[ $scenario ]]; then
-    testArgs="--scenario $scenario"
-else
-    testArgs=pkgsUnstable
-fi
-
 "${BASH_SOURCE[0]%/*}/../run-tests.sh" --ci --scenario $scenario