hack/test-unit.sh: remove this alias to cut down on scripts

This script was basically an alias for `./hack/module.sh unittest`. We even
tell people to run the unit tests via module.sh in our contributing doc.
Let's ditch it - the best line of (shell code) is the one you don't write.

An analagous change was made in CI to use module.sh in place of test-unit.sh.

Signed-off-by: Andrew Keesler <akeesler@vmware.com>

hack/test-unit.sh

@@ -1,10 +0,0 @@
-#!/usr/bin/env bash
-
-# Copyright 2020 VMware, Inc.
-# SPDX-License-Identifier: Apache-2.0
-
-set -euo pipefail
-
-ROOT="$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )"
-
-"$ROOT/hack/module.sh" unittest