scripts: container.sh: replace unusual stderr echo redirect

The command was more complicated than necessary, and somehow contained
two redirects of stdout.

scripts/container.sh

@@ -18,7 +18,7 @@ then
 	docker build -t "${TAG}" contrib/docker
 	docker run -it --rm -u "$(id -u):$(id -g)" --volume="$(pwd):/gluon" -e HOME=/gluon "${TAG}"
 else
-	1>&2 echo "Please install either podman or docker. Exiting" >/dev/null
+	echo "Please install either podman or docker. Exiting" >&2
 	exit 1
 fi