Remove ZUUL_REF

Removing old ZUUL_ env variables which have been replaced with
Ansible variables.

Change-Id: Iaeac4ac51c518fe4042a1287de16c6fafccc1d6b
diff --git a/tests/unit/test_github_driver.py b/tests/unit/test_github_driver.py
index 88408fa..ec90cd6 100644
--- a/tests/unit/test_github_driver.py
+++ b/tests/unit/test_github_driver.py
@@ -113,7 +113,7 @@
         self.waitUntilSettled()
 
         build_params = self.builds[0].parameters
-        self.assertEqual('refs/tags/newtag', build_params['ZUUL_REF'])
+        self.assertEqual('refs/tags/newtag', build_params['zuul']['ref'])
         self.assertEqual('00000000000000000000000000000000',
                          build_params['zuul']['oldrev'])
         self.assertEqual(sha, build_params['zuul']['newrev'])
@@ -137,7 +137,7 @@
         self.waitUntilSettled()
 
         build_params = self.builds[0].parameters
-        self.assertEqual('refs/heads/master', build_params['ZUUL_REF'])
+        self.assertEqual('refs/heads/master', build_params['zuul']['ref'])
         self.assertEqual(old_sha, build_params['zuul']['oldrev'])
         self.assertEqual(new_sha, build_params['zuul']['newrev'])