Bug 1580273 - Add the needed head files to support-files; r=leplatrem

Differential Revision: https://phabricator.services.mozilla.com/D45409

--HG--
extra : moz-landing-system : lando

netwerk/dns/tests/unit/xpcshell.ini

@@ -1,7 +1,10 @@
 [DEFAULT]
 head = ../../../../services/common/tests/unit/head_global.js ../../../../services/common/tests/unit/head_helpers.js
 firefox-appdir = browser
-support-files = data/**
+support-files =
+  data/**
+  !/services/common/tests/unit/head_global.js
+  !/services/common/tests/unit/head_helpers.js
 
 [test_PublicSuffixList.js]
 [test_nsEffectiveTLDService_Reload_DAFSA.js]