Add clean script to tests to remove Go executables

tests/go/clean.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -o errexit
+set -o pipefail
+IFS='
+'
+
+cd -P "$(dirname "$0")"
+
+rm -rf student
+find . -type f -executable ! -name '*.sh' -delete